I have never had a problem with them. Had a part in the wrong box once and they took care of it ASAP.
If I need one part or two, Amazon is probably the better deal because even though the part may cost a little more, the free Prime shipping makes up for it. But, I've found when ordering a stack of parts for a project (say a front suspension rehab) that RA becomes the better deal because the combined shipping is better.
Ebay can have good deals but I recently had a seller pull a fast one with trying to pass off a cheapo aftermarket (that didn't work) as the real deal. Got my money back but it was quite the annoyance. Most other times it has been fine though.
Roughly the same here... short take - I use RA in specific situations, and will do so in the future...
AMZN for a 'known' part, and especially if I want it in a day or two (Prime). I don't purchase a lot of vehicle-specific parts from them. And sometimes... I actually buy *retail* :: gasp! :: Amazon isn't going to loan me tools, as an example, and sometimes I want the part *today*.
The Bay for odds / ends / accessories /
anything 'used' (like the fuel filler door I just got for the Voy). You can often get some components here that you can't find in retail channels, due to the salvage yards having a big presence. Forget about 'bidding'...most of what I find is 'buy it now' for $X - and in a way, that's fine. When you come across a 'make offer'...buy a lottery ticket...LOL.
The one thing I take a hit on with eBay shippers is when they stick a prepaid postage label on something, creating a ton of postage due on my end - and the USPS carrier is a 'cash-only' entity. Then I have to take a photo of the package & chase the shipper / eBay down for the postage. Special note: watch for the shipping location - try and get things from US / Canada where possible. Many things ship from HK or China, and the term 'slow boat' conveys new meaning, here.
RA for big orders, or if I don't know the exact part name - as long as I know the subsystem, I can usually find it. Their parts lookup engine is very good (down to the RPO-specific options on many parts; e.g.; '9900lb brakes'), and it's easy for me to x-ref different years, etc. Like going to a parts store and finding an old-school counter rep who 'knows' many different vehicles. But from the comfort of my recliner, and no talkback...
In fact, I just got a big order from RA for the Sierra yesterday - time to go make some room in the garage and start swapping parts.
The one thing I *hate* about RA is their shipping costs. Most sites that I frequent, you eventually get a break on shipping when you reach a certain amount. With RA, the costs just keep getting more obscene, the bigger the order gets - especially when it hits 3 or more warehouses. 5% codes lessen some of that pain, but don't eliminate it.
Gotta give them credit on getting the right parts to me.
Also, their clearance sale e-mails can come in handy - you can get some vehicle-specific parts for big discounts.
I understand they're low-margin, given their pricing on the parts.
Maybe I just hate outliers...lol.