How much is P104-100 per card these days?
Bitnand.com quoted me $450 per card, which seems like a decent deal for 40MH/s. It does seem like GPU prices have come down a lot in the recent two to three months.
Ebay has GTX 1080tis for under $500 each. That is a terrible deal for a p104. 50mh for 1080ti and ethlargement.
Dude, how can you compare new cards with 2nd hand cards?

For that matter, a 2nd hand P104 is going for like under $300, which makes P104 a way better choice than 1080Ti.
The 1080 Ti remains the better choice always even if it is second hand because it was not designed specifically for mining and has bigger warranty and resale value.
All the cards that are build exclusively for mining like the P series from Nvidia have only 3 months of warranty. Guess which of both cards is build with better quality materials and has passed more thorough testing ?
Having used P106 for nearly 9 months, I personally don't see any problems with these cards. My friends also has P104 running for nearly 7 months without ANY problems, way pass your supposedly 3 month warranty concern.
Unless you have proof, I think your claims are just hypothesis without data to support it.