There is a common scam: You have a client that can only pay be cheque. You do work for them, send a bill for $5,700 and they accidentally send a cheque for $7,500. Easy enough mistake to make, so they ask you to bank the cheque and send back the $1,800.
You may be clever enough not to lose the $1,800, but you’ll never get paid for your work.
If it’s not clear: they don’t care about the work you do. It’s only the preparation for a scam.