I'm not entirely sure how cheques work being that I've not used one in about 15 years, but I'd imagine they give a cheque from an account with no money. Because cheques are awful the money will appear in your account for a time period by which you are given the illusion of getting legit money. They ask you to buy something like jewellery or gift cards and ask for it back at the end, maybe letting you keep a bit of it for yourself. A while goes by and the cheque bounces, which means you're then on the hook for the cost of everything you purchased and the scammer gets a ton of free items that they can then sell on.

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.

99.99% it's a refund scam. The cheque was probably designed to bounce.