Thing is, you never know of good or valid the warranty is until you try to claim. First hand warranty, no problem, second, third hand cards where the seller says "I'll help with the warranty", no so good.
Sure, it may be alright but has to be considered as one of the risks, your x amount spent on second hand goods may be completely lost of it fails. How much is that worth vs an iron clad new card warranty?
Abused may be a little harsh but many sellers seem to think their card is worth as much as a slightly used second hand card. A 2 year old Ti is not worth as much as a 3 month old card. A 2 year old heavily OC'd card, no thanks, but you may never know how it's been used
Weighing all the pro's and con's up of buying second hand cards, they'd have to be priced right for me to ever consider but they never are IMO. Sellers expect too much so I'd rather pick one up brand spanking new and would advised others to do the same. THink I saw a 1080 or 1070 on here fairly recently that was already being sold to a third owner and I think was priced only £30 less than a new one.