If you're a college student, you or your school have submitted the papers to Turnitin? If that's the case, they may appear as plagiarized. If not, the service may claim they were plagiarized and you'll only lose the ability to publish them on your blog, website, or whatever. My advice is to never trust the judgement or good will of services that claim to buy your essays because when you submit them for their "approval" - they are already stored in their databases. And the fact is, most of such services are from Russia or Ukraine and copyright laws don't apply to them; in other words, they can steal whatever you submit to their servers without any repercussions.

The money, if you are lucky to get any for your sold academic papers, will be negligible. You don't want to go through unwinnable fights with the third-world country legal systems if you find out some of your "rejected" essays have been put up for sale anyway.