"Too small" as in "too short"? 

Or "too small" as in diameter is wrong?  (should be 6mm)

I had a different experience.
I bought an RT1 headlight rim screw from him. Next day he sent a message stating that he looked all over his shop but couldn't find the screw. He refunded right away. I didn't leave feedback since no transaction.

Pic of what you bought alongside a genuine original would be good. Not just a yamaha updated part?. Is the seller just a middle man passing the order onto a supplier. I don't know how it works but i see some sellers with thousands of items--can't carry that many in stock surely. I'm waiting on something that tracking shows delivered in Florida & i'm in NZ. They assure me its definitely on the way so fingers crossed.

Yeah scum like that tend to so shady stuff.  I got screwed on a classic car many years ago from e-bay, later found out they've done that to a few people and they too changed their name and kept screwing people.  Of course feebay don't car as long as they get their outrageous fees!

I know that ebay adds on what bikes the parts fit. I contacted a seller about fuel pump relays advertised for 1970's DT 2 strokes. He told me that ebay adds that "(fits 1976 DT125)" note at the end.

I don't have the original part, it's the wing bolt that hold the oil tank on my 81 DT175. 

I'm in Florida, they didn't deliver it to me

I buy parts for Mopars sometimes and can tell you 100% for sure that those "(fits xxx)" are not accurate!  I know enough about what I'm buying to know they are full of crap a lot of times...

my favorite are transmission seals photographed with a Yamaha parts label with correct part number behind it

The jerk didn't have the Yamaha parts label but he did advertise it with the correct part number I got from Parzilla, the picture sure looked like what I needed so I went a head and got it, turns out it's too small, must be for a smaller bike like an 80 or something...

@ Airbornesilva, yeah I know enough also, but there might be some that don't so I tried to make it easier on those by contacting the seller about the misinformation.