guitarpartsresource and basspartsresource have had a few threads on here over the years... and i've had a few experiences with them (but will NEVER have another).
the good: great selection, great prices, fast shipping
the bad: ZERO CUSTOMER SERVICE. and i mean none. and more importantly, they have a history of selling b-stock and defective products as new, and then ignoring the customer when they have a problem. there have been a few threads on this.
My experience: first time ordering i only got a few knobs. Great transaction in the sense that nothing went wrong. I had no need to contact customer service, so yay, great job. Second order... i was buying all sorts of upgrades for an SX including a string retainer, knobs, bridge, pots, and a tusq nut. So i place the order... about 10 minutes after ordering i realized i mistakenly ordered 2 knobs instead of 3. Should be a simple fix to get them to add a third knob to be included in my shipment, no? I promptly sent a simple email, and called their number, no answer, left a voicemail. A day goes by, no response. I call and email again, no answer. I didn't leave a voicemail because I figured i'd keep calling til i reached someone. I called on the hour for 8 hours. Next day did the same thing, and emailed again. At this point I realized that they simply don't check emails, ever, and that they don't answer phone calls or return voicemails. Ever. So be it, i order the 3rd knob elsewhere, their loss. This was an acceptable albeit far from ideal situation as it was my own mistake in the beginning.
And here's where it gets hairy. So the order arrives the next day... hey, that was fast! Great, right? No. The "tusq nut" was shipped loose in the box, without any kind of markings, labeling, or packaging. For all I know I just bought a 10 cent plastic SX nut (for about $7) to replace my 10 cent plastic SX nut that had cracked. And then I look closer... the "new" tusq nut was sold as pre-slotted... but these slots were cut so low that there was no possibility of using it on an instrument. The depth of these slots was insane, at least 7/8 the height of the entire nut, rendering the product useless. I promptly emailed Basspartsresource, lo and behold, no reply. I didn't accuse them of selling shady parts (which i'm pretty sure this was), but simply told them it was defective and that i'd like to return it. No reply. I emailed dozens of times over the next two weeks, called dozens of times, and they never once bothered to reply. I came on here to post about the experience and found several other folks who had had the exact same experience with the unusable "tusq" nuts, and never being able to get in touch with someone. I probably could have had my credit card company get my money back, but i opted to eat the $7 and take it as a lesson learned. Had my local tech fabricate and slot a bone nut for me and it turned out great.
As for this company... I can't in good conscience recommend them to anyone as they literally have no customer service. I would highly advise anyone considering them to stay away.