There are good and bad sellers doing business through ebay.

I've never bought any used RC stuff from ebay sellers. I have bought a few new things.

I got a NIB OS 70 Surpass I (old but never used) and Futaba 6XAS (it was still a current model at the time) from a guy who also ran a small Kit making operation. Everything was exactly as he described it, I got a good price, and was very happy with the deal.

I got an ASP ngine from a seller in New York who I think might have been an actual hobby shop that used ebay to have a bigger potential customer base. It was a NIB engine and the total (to the door) price was right.

I bought NiMh receiver packs from one of the many sellers. It was four packs for just over the single pack price at Hangtimes (NoBS Batteries) or Radical RC. One pack had a dead cell, one cycled about 60% of capacity, one seems good, the last one is still in the drawer. I may or may not ever try to use it. No more batteries for me from ebay sellers.

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Check the "feedback" on sellers. Don't just look at the percentage, read the actual comments. If the deal seems "too good," it is probably bad. Do not expect any kind of customer sevice from a seller. Most used items are sold "as is" so there is probably no recourse if you get junk.