If you gradually increase the sales amount, and have a long standing paypal account. It won't have any issues as it won't be suspicious. But if you start getting huge chunks of money overnight without gradual progression, the automatic system in place at PayPal will see it as a red light and inquire into it.
PayPal is a service provider and deducts a good fees in %age, so the more money you make, the more it makes. It's business, and they like it. They are the biggest payment processing company online with international eyes on it, it just has to look doing things right.