In the agreement you agree to their terms. If you violate or are even suspected of violating their terms, then you could be subject to account closure-- which can be very upsetting if you have not moved funds from your paypal to some other more conventional account.
This link has some good and relevant information.
http://www.sitepoint.com/forums/ecommerce-5/paypal-closed-my-account-after-10-years-wonderful-service-686030.html
Or just Google "paypal closed my account".
Paypal is fine, I have one and am happy with it. I just am intelligent about using it, and advise you to be the same. If I know I have money coming in, I keep an eye out for the e-mail they will invariably send me. Then I claim my funds shortly after the e-mail arrives. It is not so bad to have your account closed with $0 in it, so just make sure your paypal has $0 in it as much as possible...
If I had more payments coming through, I might attempt to claim my funds once or twice a day regardless of emails.
Take care,
-Brad
As a side note, there are other services worth looking at similar to Paypal and for businesses Paypal is not as good really as a real merchant account which often provides more consideration in regards to the business relationship and may allow more opportunity for you to contest unfair decisions against you.
