I once bought an engine from a website Japan Star Motors, and they sent me a big a$$ paper weight as the engine knocked like hell [which I didn't realize until after I installed it in my car.
They promised to send me another one but I kept getting put off. Until I demanded a refund which they agreed on but never credited me for it. Since I bought it with a debit card and a month or more had already passed I coudn't do anything about it.
I contacted the BBB but they told me that every state has there own, So I contacted Maryland's BBB which all they had was an email address, which took two weeks to get back to me so now its like 3 months later and it turns out the company went belly up [I wonder why?].
What I learned, only buy from a reputable company usually those that mechanic shops have accounts with.