If they are mailing payment, how are they picking up the horse? Just because your bank lets you draw cash on a check you deposited, it doesn't mean that it cleared. They can take days, weeks or occasionally months to bounce. Then the bank debits your account and you are left holding the bag.
Last year I sold a saddle online. I ended up selling it to a person I know on a Haflinger forum so the check was good. However, I still get e-mails that go something like this:
Hello, My name is Carl. I am much interested in the saddle you are having for sale. Do you have more? I will buy some saddles. The saddle is $400. I unable to get payment check that small to you. I will send $700 check for each one saddle you to me sell. Please then you may send to me back surplus $300 for my extra. Please tell to me if this is agreeable for you. I need saddles and answer very soon.
Sincerely,
Carl
I get a few of these every month. It's a scam.