There are only a few sellers who are decent people and will disclose how the card was actually used. Most people will just sell them without disclosing the issues. Even on TE market place, it feels risky to buy a used GPU for above reasons. And when the pricing is somewhere around 75-80% of new for a 1-2 year old card, it just doesn't feel like a good deal.
Don't get me wrong, that's a decent level of discount for 12-18 months of usage. But given the high risk nature of current used market, it's not enough. And when these cards come without warranty because the seller doesn't have the invoice, that takes away whatever attractiveness these cards had.
Personally, for me, if a new product comes with 3 year warranty, the used product not having warranty automatically devalues it by 25-30%. Then you have to factor in the depreciation, which for GPU should be at least 25% for the first year. So for me, a 1 year old RTX 3060 without warranty is currently worth 20k, with warranty it's worth 30k.