PayPal isn't a bank. They're a processor. People run a fowl when they keep large amounts in their processor account instead of doing free nightly sweeps. They also run into trouble when they do weird things - like new accounts receiving large funds from international sources, etc. PayPal (and all processors) are required to investigate those instances until you have an established relationship with them - and they'll temporarily hold the suspicious funds while that happens. Business accounts have predictable, established patterns.

99% of the horror stories you hear fall into one of these categories, or both: 1) New Account 2) Unusual Account Activity

PayPal processed millions in annual payments for my previous company, without any issues.