If I flash a bad ESN iPhone 4 to cricket will I be able to fully use the phone?

Thinking of buying a iPhone but can only find bad ESN ones. Does it matter? My carrier is Cricket so I was just going to buy the phone and flash it. Will I be able to use the phone like an iPhone should be used?

They are probably stolen. I wouldn't buy one and expect to use it as a phone on any network.

Buy a legally owned phone that has a clean ESN, if you want a phone.