I suggest you take that lock off immediately. You don’t have a right to simply lock out another tenant because he has not paid his share of the rent. Doing that can cause you serious legal problems. While you don’t have a written lease, you do have a verbal lease agreement. He is a sub-tenant and you are his landlord. You need to go follow the proper eviction procedures to get him out, you cannot just lock him out.
Absolutely not. Taking his stuff and selling it would amount to theft, and you definitely do not want to wind up facing prosecution for a theft offense over this. To get your money, you need to sue him for it in court.

