Are you talking about Weapon Creator or WCS?
if you buy from a third party the usual procedure is that you pay for it (I generally use Pay Pal) then the developer will sent you an e-mail containing the download or a link to the download.
After you get it be sure to e-mail the developer and thank him or her and let them know that you got what you paid for so they definitely have confirmation of it.
They will appreciate it.
So make sure whatever e-mail address you give them will work and that you mark it or whatever you have to do so it goes into your inbox and not your spam folder.
