Buyer beware, the NFL's free agent period is almost upon us. Teams are free to negotiate with and sign free agents when the new league year begins at 4 p.m. on March 18.

Teams generally enter free agency with one of two goals. Either they want to sign players and improve their roster, or they at least want to retain their essential pending free agents. Sometimes teams get duped into signing players to long-term, lucrative contracts only to regret their decisions later.

The following five free agents all want paydays this offseason. However, teams should think twice before spending millions of dollars on these players.

5. Ronald Darby, CB

The best ability is availability. Whatever upside Darby brings on the football field is eclipsed by his frequent absences. Since entering the NFL as a second round pick in 2015, Darby has missed 23 games. He's played in 28 games over the past three seasons and missed 20.

Last year, Darby stood out as one of the best free agent cornerbacks in the NFL. That is hardly the case this offseason. With Chris Harris and Byron Jones drawing all of the attention, fans largely overlook Darby's free agency. Other free agent corners, like James Bradberry and Bradley Roby, push Darby even farther down the free agent spectrum.

However, there are never enough cornerbacks in the NFL. Teams always need more coverage experts, and someone will reach out to Darby when the other top corners quickly get snatched up.

In March of last year, the Philadelphia Eagles signed Darby to a one-year $6.5 million deal. He shouldn't get that much money this time around.

4. Jadeveon Clowney, DE

When the Houston Texans and Clowney got into a battle last offseason, a key issue was whether the Pro Bowler classified as an outside linebacker or defensive end.

Clowney wanted the defensive end classification because he could make more money under the franchise tag ($17.13 million) and on future contracts. Houston classified him as a linebacker, which paid out $15.97 million under the tag.

Eventually, the Texans threw up their hands and traded Clowney to the Seattle Seahawks. He moved to defensive end full-time. Now, with his year under the franchise tag almost over, Clowney can chase a massive multi-year deal.

However, before NFL teams fall in love with Clowney's physical capabilities, they should double-check his production. The 2014 first overall pick recorded just three sacks and 13 quarterback hits in 11 starts this past season. He's never crossed the ten-sack barrier in his career either.

Playing in Houston's 3-4 scheme did prevent Clowney from rushing the passer consistently because he had to drop back in coverage sometimes. However, except for two or three games, Clowney looked passive and ineffective in Seattle's 4-3 defense.

DeMarcus Lawrence makes $21 million per season on his current contract. Frank Clark makes $20.8 million, and Trey Flowers makes $18 million annually. Arguably, none of those players are worth that kind of money, and neither is Clowney. Yet, that's the kind of payday he could demand this offseason.

Per ESPN's Josina Anderson, Clowney wants to return to Seattle in 2020 if he receives an acceptable deal.

3. Shaquil Barrett, OLB

Barrett signed a one-year, $4 million contract with the Tampa Bay Buccaneers last spring. The Buccaneers got far more than they paid for as Barrett turned into one of the NFL's premier pass rushers in 2019.

Barrett, an undrafted free agent from Colorado State, led the NFL with 19.5 sacks and tallied 37 quarterback hits. He more than doubled his career totals in both of those areas. Barrett's name floated around in the Defensive Player of the Year conversation for several weeks.

While he played phenomenal last year, Barrett is a prime example of a potential one-hit-wonder. The man only had 15 starts in his five seasons before arriving in Tampa Bay. No one, certainly not the Buccaneers, expected he would transform into an All-Pro pass rusher.

In 2019, Barrett recorded three or more sacks three separate times. Previously, he'd never registered two sacks in a game in his career.

NFL players can certainly develop into explosive stars, but Barrett came out of nowhere in his age 27 season. That at least warrants some caution from teams.

Plus, keep in mind, Barrett has never made more money per season than what he received this past year. He could try to make up for lost time and go hunting for one of the largest outside linebacker deals in the league. For reference, Chandler Jones, who finished behind Barrett with 19 sacks this past season, makes $16.5 annually.

2. Arik Armstead, DE

The San Francisco 49ers made the right move when the team picked up Armstead's fifth-year rookie option. The 6-7 Oregon product made just North of $9 million this past season. However, he could seek an even larger payout in free agency.

After producing nine sacks and 29 quarterback hits through his first four NFL seasons, Armstead erupted in 2019. Starting all 16 games for the second consecutive season, he recorded ten sacks and 18 quarterback hits. Armstead also set career-highs with 54 tackles, 11 tackles for loss, and two forced fumbles.

Similar to Barrett's situation, no one knows if Armstead is capable of replicating his production in 2020. The former first round pick played on a loaded defensive front, which may have inflated his numbers.

Los Angeles' Melvin Ingram signed a four-year, $64 million contract extension after posting eight sacks and 19 quarterback hits in 2016. He's making $16 million annually on the deal. Armstead could demand a similar contract in free agency, although his track record is much less consistent than Ingram's.

1. Bud Dupree, OLB

The Pittsburgh Steelers took a chance when they picked up Dupree's fifth-year rookie option. The 22nd overall pick in the 2015 NFL Draft only produced 20 sacks and 33 quarterback hits in his first four seasons.

Dupree exploded in 2019. Alongside First Team All-Pros in Cameron Heyward and T.J. Watt, Dupree finally delivered on his potential. The Kentucky product started all 16 games for the first time. He also set career-highs in tackles (68), sacks (11.5), quarterback hits (17), forced fumbles (four), and fumble recoveries (2).

The Steelers led the NFL in sacks for the third consecutive season thanks to Dupree's emergence. However, after one good year on a stacked defense, NFL teams should not buy into Dupree as a consistent player.

Sacks are one of the most deceptive stats in football, hence why three of the players in this article are pass rushers coming off of big years. Sometimes conditions line up perfectly, and pass rushers get hot. That is likely the case with Dupree.

Quarterback hits serve as a better predictor for consistency. Dupree posted 17 this past season. Despite finishing the year with only five sacks, DeMarcus Lawrence recorded 16 quarterback hits. Over the past three seasons, Lawrence has 65 quarterback hits to Dupree's 37. Lawrence is a significantly better defensive player than Dupree, even with his lackluster sack total in 2019.

This past season, two players recorded 37 quarterback hits. Dupree finished with the 29th-most quarterback hits, showing where Pittsburgh's outside linebacker ranks in the pass rushing hierarchy.

After one good season, NFL teams should not buy into the hype surrounding Dupree. More than likely, he will revert to his previous form in 2020. Paying him the same kind of money as a Ryan Kerrigan or Za'Darius Smith could prove disastrous.