Is there anything you can do early on to avoid PayPal freezing or limiting your account without cause?

Paypal account are blocked for a reason. Always a reason. You might not agree with the reasoning, but its there.

Paypal likes organic growth of your account and your relationship with them. Everyone does. Introduce a financial anomaly, this will result in triggers / alerts that go off in their system, which can lead to an account being block, until further review.

If your transaction history on Ebay (for example) has been averaging transactions of US$ 50, a US$ 5,000 is an anomaly. Its not necessarily wrong, but just that Paypal wants to play it safe.

What has made this experience bad for everyone else are two things (in my opinion):

• Not knowing the rules. Please do spend time and read up on AUP, TOS, etc. For example using your PayPal account on a website to say send money overseas (as a service) is not allowed. Or using Paypal account as a proxy for others, not allowed. If you're not cognizant of the acceptable usage policies and the terms of service they provide, only you are to blame. The best advice is - when in doubt - check it out!
• The second, yet equally important factor is the Customer Service. Yes, it absolutely sucks (if you're not being helped out). This lackluster service by PayPal is then further amplified in the powerful echelons of user forums across the interwebs.

Keep a steady organically fed relationship with Paypal, and within the prescribed AUP/TOS, and you ought not to have any problems.