I will leave an unpopular tip for you guys.
Avoid payment gateways that operate on "instant approval", "get started now", etc...this includes Stripe, PayPal and some of the major payment processors used.
I will explain: if you want to sell on Stripe, just create an account, fill in your details, verify your identity and you are all set. This takes less than an hour and you are ready to sell.
The problem with that: they don't analyze your site. It is all automatic, fast and supposedly simple. After a few dozen sales, depending on the niche/type of your site, you get an email saying that your money is withheld because the processor does not support your high-risk business model, including things like SMM, dropshipping and several other popular business types on BHW.
What to do then? It's boring, tedious and time-consuming. But it's better if you fill out all the data, answer all the questions they'll ask about your site, and get 100% approved at a payment processor that it takes a week or two to get your account fully approved and verified to start selling.
That way, your business model will be immediately disapproved or approved, and you will avoid money retention problems. Some examples of payment gateways that require submission of documents + additional details about your site + extra questions + submission of invoices, etc. are Ocean Payment, Paymentwall, 2Checkout, etc.
If you want something long term, consider spending a few days and not just a few hours to build up a really solid account with a long term payment gateway.