I too had a dreadful experience with US Auto Parts ('USAP'): i ordered a part and paid for it (in retrospect, i should have been suspicious when the price was so much less than elsewhere, even the OEM!?) but when it hadn't arrived about three weeks later i emailed them, repeatedly. None of my emails were answered so i rang them (at 3:00AM my time!) only to be told that they didn't have it in stock. I then (foolishly) agreed not to cancel the order upon condition that they could assure me that the part was dispatched within 48 hours. And that apparently happened.
However, the second chapter of the fiasco began a couple of days later: UPS sent me a message confirming that the goods had been delivered to USAP's shipping 'partner' Bongo International but when i tried to contact Bongo a week or so later, they, like USAP, refused to answer my numerous emails. Days later, Bongo eventually replied by informing me that they knew nothing of the delivery. Multiple emails were then exchanged until they alleged that USAP had sent them something but it was an entirely different item from that which i had ordered.
It was only after i filed a complaint with the Better Business Council that, surprise surprise, Bongo located the goods (the one i had in fact ordered and at the depot which UPS had notified about me and which i in turn had informed Bongo) and that it'd be dispatched promptly. However, following delivery of the goods to me i went to my online bank account to discover that Bongo has charged me over $90 for the privilege of dispatching something (a door switch) that weighed barely 8 ounces and about the size of a pencil case!
I again submitted a complaint to the BBC and, again, Bongo emailed me to apologise for their abominable service and offered me a much reduced delivery charge (by way of a partial refund).
Had i any idea these two firms were so deceitful and incompetent i, obviously, wouldn't have gone anywhere near them. And i advise anybody contemplating doing business with them to think very hard before doing so.
[I haven't had time to install the part yet so I'll not be at all surprised if it doesn't work. If it doesn't, i won't be going through the hoops of tyring to get my money back ... enough's enough with these shonks!]