Why have you changed your mind?

I think you had better have the best excuse as to buy something means you have agreed to the terms and conditions of this site and legally are obliged to.

There is a process in place for you to do this and its honest and not fraud. (I hope you know that cancelling a check is fraud)

Contact the seller as a lot of them have a return policy and it would be good to let them know ASAP as they may have already posted your item, thinking they are dealing with an honest and upright person.

Also be prepared to be on a lot of black lists after asking this question.... or give the best excuse we have ever heard.