"House hacking" turned bad

[Mike D.]

so I have been renting out rooms in my first house to two acquaintances. One has been out of work for a while and is home all day(trust fund baby). 

apparently he has been selling weed out of my house. I reamed him out when I found out. I told him if I find out it's still going on, he's out no questions asked. He reluctantly said "you're right, I'll stop".  I'm not an idiot, I fully expect it to continue. The lazy *** is home alone all day. 

What would you do? Set up a hidden camera?  I'm at work all day and can't think of a better way to catch him