Handing out free agency grades is like evaluating a guy’s pickup lines, because there are scarce few hits in a sea of empty promises.

Just look at last offseason, when the Buccaneers earned the highest marks from most evaluators. Tampa Bay’s big catches included Josh McCown, Michael Johnson and Anthony Collins, all of whom have since been released after helping the Bucs achieve the worst record in the league.

Tampa Bay was not the only team to strike fool’s gold. The Raiders got solid reviews, as well, after fixing their defense by signing LaMarr Woodley, Justin Tuck, Antonio Smith and Tarell Brown. Oakland finished with the league’s No. 21 defense and a 3-13 record, one win less than the season prior. If the Raiders hadn’t hit on Khalil Mack and Derek Carr in the draft, things could have been even worse.

These bottom-feeders were not the only teams to have free-agent additions come back to bite them in the rear. The Chargers thought they were loading up their running game by signing Donald Brown to join a backfield that already included Ryan Mathews and Danny Woodhead. Instead, Brown averaged just 2.6 yards per carry and San Diego finished with the second-worst rushing offense in the league.

Jared Allen is another example, as he was supposed to be the missing piece for Chicago’s pass defense. Instead, the entire Bears defense went to pieces, with Allen finishing with the fewest sacks (5.5) of his 11-year career.

The reasons for these backfires are numerous. Sometimes players do not fit in as well in their new scheme or new locker room. Sometimes they get lazy after signing fat new contracts. And sometimes, as in Allen’s case, old age finds them in a hurry. There are potential land mines everywhere, which is why so many successful organizations have gone the “draft and develop” route.

“The draft is your lifeblood,” said Chargers GM Tom Telesco. “Those are the players you can really hand-pick into your system and groom in your system. You can’t do that as much in free agency.”

It’s wasn’t all doom and gloom on the open market. Steve Smith played a big part in the Ravens making the playoffs in his first season in Baltimore. Another receiver, Golden Tate, helped drive the Lions into the tournament with his 99-catch season. And just so we’re not giving all the love to skill players, Jared Veldheer was a big reason the Cardinals were able to withstand an ungodly rash of injuries and still qualify for the postseason.

The Broncos were also big players in free agency last offseason, adding Emmanuel Sanders, Aqib Talib, DeMarcus Ware and T.J. Ward. Those players helped the Broncos to a 12-4 record and a fourth straight AFC West title, although Denver got Peyton Manning-ed again in the postseason. Things quickly came full circle, though, as the suddenly cash-strapped Broncos have lost Julius Thomas, Orlando Franklin, Terrance Knighton and Rahim Moore already this offseason.

“I think what we’re really seeing this year is the idea of what the CBA [collective bargaining agreement] was meant to be and that was get more cash into the veterans’ hands,’’ said Broncos executive VP John Elway. “Look at the wage scale and all that money is cycling through to the veterans. [It’s] a little hard to get used to, but that’s what the NFL is about now. [Teams] do that with more confidence, knowing what they’re getting. … You’re seeing teams with more money now … so they are able to put more money out there for veteran they know what they can do.’’

The inherent problem with free agency is that teams do not let talented free agents in their prime hit the market very often. When that happens, bidding wars ensue that result in drastic overpaying. The two biggest free agents to switch teams this offseason — Ndamukong Suh and Darrelle Revis — signed contracts that combine to top out at $184 million.

Which teams best navigated these muddled waters this offseason? The Bills have to be excited, adding LeSean McCoy, Percy Harvin and Charles Clay to an offense that desperately needed more playmakers. The quarterback situation is still a question mark, but the additions of Matt Cassel and Tyrod Taylor provide options and competition.

The Texans also made some nice acquisitions, adding Vince Wilfork, Rahim Moore and Cecil Shorts. The team also picked up Brian Hoyer to compete with the re-signed Ryan Mallett … if either of those QBs plays up to his potential, the Texans are going to the playoffs.

However, the real winner in free agency is the team who has yet to sign a player from outside its organization: the Packers. Green Bay re-signed WR Randall Cobb and OT Bryan Bulaga, arguably the top available players at their respective positions. GM Ted Thompson is never much of a player in free agency, which means he never loses big money on high-priced gambles. Because of that, he has enough cap space available to re-sign his owns stars when they hit the open market.

And that’s the trick with free agency … the only was to earn an “A” is to record a “DNP.”