PayPal, Stripe, Square Payments, Amazon Payments, heck... none of them care if you're a legitimate business or not unless you're doing crazy amounts of sales. But, at that point, you'd want to move away from the popular payment solutions and onto something like Authorize.net, Braintree, or one of the hundreds of others out there - just stay away from CyberSource. Horrible developer relations there.
That said, I'm a freelance web developer. I have an LLC to protect myself from potential legal consequences of horrible clients, but otherwise, in the states, you can operate under your own name and SS# for business purposes. Just know that, if someone like Marshall were to come after you and sue you for damages, without an LLC, you're basically saying "if I lose a court case and can't pay the resulting fees, you can take my car, my house, my guitars, everything, to pay for it." With an LLC, you're only liable for your own business assets. I have a business bank account that I keep about $4 in. If someone were to sue me, they can have it. I file as an independent for tax purposes, which does cost more, but costs less than hiring an accountant and having to deal with that whole side of the business (I'm sorry, but accounting is just horrible, and it's not real math).
$10k is a little steep for reporting purposes, but I know where that comes from. As an individual, if you make less than $10k a year (but I believe that is actually a lower number, like $8k or $6k) TOTAL, from all sources, you don't need to report. Otherwise, if you make at least $600 from a single source, you're required to report it for taxes.
This is all US law and workings and procedures and such, and everyone's business model is different - I'm offering a service, vs. offering a product, and that makes a difference somehow too. I have a friend (another web developer) that works as an LLC, but files as an S-Corp, and apparently saves a lot of money on taxes. However, he spends a lot of money on an accountant, and he has to continually put money into his business, and cut his own checks to himself. Not my idea of something I want to do.
I would advise speaking to a lawyer. Find out what your options are for where you are, what the best course is, and, if it is a retailers license of sorts, have the lawyer work up a legally binding document. This way, you can make sure you get paid if you decide to sell them through another retailer.
It's all confusing as hell, I'll admit, but best of luck. Feel free to shoot me a message if you have any questions.