Can I use an iPhone 5s from AT&T and switch it to Verizon?

Can I use an iPhone 5s from AT&T and switch it to Verizon? - 1

Yes, usually if you get the phone cracked, alot of shops can do it for you.

Yep! They usually just switch the SIM card at the store and you're all set. I did it the other way around at that's what happened.

As long as the contract is paid off and its not locked or blacklisted.

You can't. AT&T is GSM and Verizon is CDMA, they're not compatible.