|If their current place looks like this, they will live like that in your place later.|
If you're a tenant, don't do these things. If you are a landlord, watch out for these things; it will not end well.
Dave Van Horn has managed rental properties for over 25 years, and has developed some sure signs of trouble to come. I have seen some of these signs in tenants I approved when I did not know better. Those were the bad tenants that I later had to file eviction proceedings on. Had I known then, I could have avoided them and saved myself a lot of money.
Easiest one: if they don't have the security deposit up front, they will have trouble paying the rent later. I learned that one the hard way.