Let me guess, they followed up by saying "but this XYZ never fails! and I have one in stock in your size". Cervelo bikes are fine, they probably don't have a higher rate of defects than any other big brand. Aside from the issues slowman mentioned, I've seen a lot of their R3 frames with the threaded bottom brackets with delaminating shells, some of the first generation BBRight R3's also had problematic downtube cable stops that would come unriveted.

As far as used bikes, I wouldn't buy one of any brand unless it was from The Pros Closet/store demo or someone I knew was selling it to me.

The "only" problem i had with my P5 was with the BBRight bottom bracket. Could never get it right, and had to ignore the bad running of the BB (i installed it myself). Two months ago I decided to mount a Power2Max and I looked at the BB again: the left one was really rotten in that it turned very unsmoothly. So I decided to replace it again, and after I arrived to demount the old one, with a lot of effort, I just looked out of interest in the carbon seating of the frame and discovered the reason of all of my problems.
There were, on the left and on the right, obstacles (metal rivet and carbon material) at a distance of 15mm from the outside and my bottom bracket is pressed in for 20 mm. So logically i hardly got the BB pressed in and they deformed such that the running of the balls in the races were badly influenced.

Either Cervelo did not know at the time about BBs entering further than 15mm or I had an insufficiently finished frame.
Anyway, after I grinded the seatings of course there was no problem pressing in the new BB and for the first time in 4 years I have a normal BB. I do not noticably cycle faster, so I guess the goodness of the BB is of minory importance.

Wolf Fork issue was 2002, if I'm not mistaken. Same era as the carbon seatpost problems. Also, right around the time that they built an in-house testing lab that would rival EFBE's (https://www.efbe.de/).

I'm somewhere around 80,000 miles into my 2004 aluminum soloist. Honestly, I kind of wish something would fail as I'm too cheap to replace a perfectly good bike.

I've had an S1 "fail" on me with some cracks near the seat tube collar. This was one of the known issues with this bike. Fortunately it got replaced by an S2.