if you want to know who’s bought your file just provide him with a reason to tell that to you.
For example. make some intentional bug in the item, bug that can’t be detected by the reviewer (else your item will not get approved), but that bug should drive the buyer crazy and contact you about the issue.
Then you just ask for forgiveness for the “mistake” you’ve made, and provide him with a update. Mean time you get to know who it is.There’s a “small” chance that the person will never buy anything from you in the future, or, this will happen more rarely, come back after you to kick your butt. But this its a small price to pay for knowing who bought your files.
Or you can simply embed some artfully hidden text(a dynamic textfeild that won’t pop up as a symbol) in your SWFs and then do a google search on the embedded text…Google can crawl SWFs now…Great technique for trackbacks…