Rock Auto has managed to piss me off every time I've ordered from them.
For example, one time I ordered two sets of brake pads, new retaining clips, and some brake pad lubricant. The next day I got an email saying the pads were unavailable but they shipped the clips and lube. The shipping they charged me for the clips and lube packets was more than what the products themselves cost. I still had to go to a local parts store to get pads, I could have got the clips and lube there without shipping charges...
Every shopping experience with them has been something similar. Another time was when I mangled my radiator off-road. I wanted to buy upper and lower hoses form them. The lower wasn't in stock but they shipped the upper to me before they told me the lower wasn't available so I paid about 50% of the cost of the hose in shipping charges and still had to source the lower hose locally when I could have got them both locally cheaper.
My guess every business has it moments and issues.. Rock Auto in general in pretty good about stock and shipping process and charge to pay pal account.
End of November 18 I ordered spark plugs for my car and shipment was lost between the store and shipper..so took a couple WEEKS to sort out.
Meanwhile I just ordered another set of 6 and received in 5 days. Impact was on paypal account and not credit card for return of NOT received parts.
I use Rock all the time. Every shipment includes a magnet and my air compressor is covered with them. I only had one issue in 15 plus years that was really a post office issue. The sent a replacement priority mail.
5% is all over the net. If you get lucky, you will find a 10% code. Great company, I have been buying from them for years and they have never let me down.