so the check is bad, but it takes several days for the bank to notice apparently. and for some reason, when they do finally notice, it's your problem not theirs?

there are several ways this one could have worked, depending on the next step.

the typical scam is: the scammer sends a check for way more than they're supposed to, then they ask the victim to refund the difference, but the check was bad. by the time the victim figures out the check has bounced, the scammer's got the money that the victim "refunded".

in this case, likely the potential victim would either have been directed to a storefront that's affiliated with the scammer, where they can sell you $6,000 worth of junk. then the check bounces, and they have all the money you just spent.

or, they send you to real jewelry stores to buy real gold and diamonds, and you don't notice the check has bounced until after you've mailed them away.