Draft expert Mike Mayock drew upon the commonly used phrase when discussing Coples at a press event Wednesday.
"He can be an All-Pro, and I don't deny his talent," Mayock told reporters. "I just say, 'buyer beware.' "
That buyer turned out to be the Jets Thursday night. They'll soon find out which end of the boom-or-bust equation they're on.
If Coples shows the kind of promise he did for scouts in the Senior Bowl, they will have hit on a pass-rushing phenom they've needed from Day 1 of the Rex Ryan era.
But if he shows the kind of inconsistency that often marked his 2011 season at North Carolina, when he had only 7 1/2 sacks after getting 10 the year before, they risk failure at a position they absolutely needed to address in a big way.
Ryan clearly believes he can and will get the most out of Coples. Ryan remains at heart a terrific defensive mind, and he envisions in Coples the kind of pass-rush brilliance that often means the difference between a good defense and a great one.
The Jets haven't had the kind of dynamic edge rusher that Ryan covets, so it will be interesting to see how he incorporates Coples into his defense. He's hoping Coples will be to the Jets' defense what Terrell Suggs is to the Ravens': a fierce outside rusher who can create havoc by getting to the quarterback.
That's the upside and promise of Coples, who at 6-6, 284 pounds and with 4.7 speed in the 40 is a physical specimen with all the tools required to be dominant. But it's what goes on inside Coples' head and his heart that is far less quantifiable and far more difficult to predict.
If he shows the hunger and relentlessness that all the great defensive players possess, the Jets have found themselves a star. If not, they may have another Vernon Gholston.
Mayock fears the worst.
"I've never liked his [game] tape ," he said. "I wouldn't draft him. But I do recognize the talent. He showed it at the Senior Bowl when he was motivated. I get nervous when guys have bad senior-year tape but great Senior Bowls. It tells me there's a money drive there."
Shortly after the Jets' pick, Mayock reiterated his skepticism. "I never liked his tape," he said. "I wouldn't draft him."
Ryan loves to prove the doubters wrong. He tried and failed to turn Gholston into a productive player; the former Ohio State linebacker finished his ill-fated three-year career with the Jets with zero sacks. But that will be in the past if Ryan can get the most out of Coples.
"I'm just working hard and doing the best I can to be the best athlete in the NFL as possible and I think it'll be great for the Jets," Coples said after being drafted.
He said Ryan had told him if he still was on the board at 16, he'd be a Jet. "I'm thankful he's a man of his word," Coples said.
Now it's up to the big defensive end to justify that faith by becoming a player who can make the big play, the kind of player Jason Pierre-Paul, another boom-or-bust player, has turned into for the Giants.
Two years ago, the Giants took the little-known defensive end out of South Florida in the first round. JPP was a big factor for them when they won it all last season.
Coples now has that chance for the Jets. They desperately need him to make it work.