I don't really have a particular seller, just bought whatever I though was reasonable didn't even check their feedback really. Some might say no returns but if your arrived item does not match their description than PayPay will resolve it in your favor. Never had a problem with lenses but with some other item.
Honestly, I haven't used Mir 1 that much, in my opinion it's pretty good lens but it's one of those lenses where it almost requires one with better photography skills, in other words it's not as easy to use as say Helios 44 series. Mainly the view is larger and focusing in low light is more challenging if you don't adjust preset aperture back and forth. At f2.8 it's a little soft but gets sharp at around 4. Overall I'd give it 7 out of 10. For how much they go for, it's worth at least play with.
Not the best photo (or beer), but a quick shot indoor.