Use different address and different account. Mix the coins if you want to get extra privacy.
you mean different receiving address?
is there no way to change the sending address?
also, the site dent require sign-up so different account is out of question....
If you use one account and send BTC from different addresses or change deposit address(if possible), what is the use? Also, I don't understand why you need to create more than one accounts. Defrauding?
P.S. Now I understood you are talking about deposit address. The answer is, if the site allows you to create new deposit address, you can. Else, you can't.