I've seen air tight tubless and gradual loss. Like you, I lose about 3-5 PSI per day, but going pretty much flat in 48 hrs is not how tubeless works. If a proper tape job was done, the valve and tire seated properly and a good quality sealant used, it should hold
Mumbling about the warranty is a troubling sign. Could be for a number of reasons, but a few that come to mind is:
He's not an authorized dealer.
He changed out some parts (like tires)
Or
Cervelo will blame the mechanic for poor workmanship.
Either way, you spent some coin for that bike, you are not being unreasonable asking for perfectly working bike, but at the same time you don't want to burn bridges. Try contacting Cervelo directly and see what they say.