In 20 years of ebay buying i have only once had an issue with a product or vendor. That was with a Tektronix 496 Spectrum Analyzer that had been advertised as working well and meeting all specs, turned out it had been cobbled together from mismatched parts taken from several Tek 49x analyser models, most noticeably a 2nd local oscillator from a lower-end 492 model. eBay and PayPal (always pay with PayPal and a credit card on eBay) backed me up 100% .
I have purchased numerous parts for my P.O.S. 1998 SL500 (the most frustrating car I have ever owned¹) from eBay vendors and have never had a problem. Check the vendor's feedback before purchasing, and alway pay with a credit card or through PayPal using a credit card--and remember that eBay does not sell anything. it is just a platform from which individuals and vendors sell stuff.
¹ - I purchased my 1998 Mercedes SL500 in July of 2014 with 53k miles on it. It was a one owner car (a couple in Palm Beach), always garaged and was in VG+ condition inside and out--full documentation of all maintenance and the original window sticker were provided--CarFax verified all this. It had just had a new top and new top hydraulics installed in January of 201--which in hindsight should have sent me running.
Why does an always garaged 16 year old $101,275.00 car with 53k miles nee a new top and hydraulics? TUrns out it is because this particular model of Mercedes is a piece of crap--developed during their silly marriage to Chrysler, and while the "green" party was calling the shots in Germany. All the plastics and synthetic materials were engineered to be biodegradable; and they did and continue to--interior and engine parts (cam oiler tubes, timing chain guides...)
It is fun to drive, and very classy, but what a PITA to own !!!