Merchants don't use google or amazon(or any other payment system) because they require a higher amount of reserve and/or fees. The loud complaints are from people who want their cake and eat it for free. People don't realize nothing is free.
The problem here is that people are generally unaware of a potential 6 months lockdown if paypal raises a red flag on your account. Furthermore the reasons for red flags are also unpredictable(Im assuming that paypal doesnt want its fraud detection scheme gamed).
The biggest problem is a difficulty/impossibility of a resolution process other than waiting for 6 months to get your funds. I would definitely try to get somebody on the phone and escalate the problem as contacting email support will get you into an infinite ping pong of templated answers.
The reasons are perfectly predictable. PayPal's risk department acts like any other merchant processor's risk department. The things that trigger a review are...
* >1% monthly volume chargeback rate
* >1% monthly volume refund rate
* too many payment disputes
* violating the terms of service (including what types of products may not be sold through PayPal)
* selling products or services with known high chargeback rates
* a sudden increase in processing volume
* a sale an order of magnitude larger than your average ticket
* accepting payment too far in advance of shipping a product or providing a service
I'm sure there's also some program in there looking at interactions between accounts to find strange patterns, but that's not usually what trips people up unless they're actually laundering money or factoring. It's always the obvious stuff.
