There are no free payment gateways or free merchant accounts. How you actually process a credit card will vary as each payment gateway and third party processor uses a different API. No audit or anything like that needed.
And it's not true that you need to process thousands of transactions for a true merchant account to be worthwhile. There are many factors that influence which is better for a business. You need to weight your options before choosing a provider.
I wasn't suggesting that a true merchant account wasn't worthwile, just that I have been informed that to process credit card numbers on your own site you have to have an audit, using a PSP you don't need to have an audit as the PSP is processing the credit card number for you.
With Protx you still need a merchant account with your bank.
For a true merchant account a credit check will be done but that's not a big deal. Considering the benefits of a true merchant account over a third party processor, under most circumstances, it is usually well worth doing.