Yes, those look like aftermarket HD800 pads that cost $12 with shipping included. If the seller sent you those by mistake, complain and he should send you correct ones without you having to send the wrong ones back. At least that's been my experience with sellers from China. It can take some (or a lot of) time, but eventually you should either get what you paid for or your money back.
But look at it this way: if you bought HD700 new, didn't find the sound quite perfect and wanted to experiment with different pads, you would still do the same thing (buy a number of different pads, spend money on return shipping etc.). On the other hand, why would anyone buy these (or any) cans used and obviously quite worn for $300 if you can get new ones for $350-$390 is beyond me. I did get mine used without pads and baffle rings, but the total cost including new pads and baffle rings from Sennheiser for me was about $265, and the lowest the new ones dropped around here was about $500. For me paying about half for a used product is OK, paying 75-85% of the price of a new product is absurd. Even if the initial retail price was much higher, now it's not. So I completely agree, buying used for $300 is not a good idea if you can get new for not much more.