In theory I bet it's an efficient option. But I'm curious about the risks and costs involved in dealing with such "services", and how easy it is to find reputable thugs.

I used to know a guy who had an impressive physique and foreign accent and was hired for similar "communication jobs" (debt collection). It was all above board so he didn't carry any weapons and didn't do anything but the mere implication in his presence was often enough to motivate debtors to find ways to pay shortly after his visits. He was actually a nice guy and not much of a fighter.

Sure. Although I guess the occupiers can also hire thugs to beat the owner up with baseball bats. There are reasons why this form of dispute resolution has gone out of fashion in the kind of countries you might want to live in.

You can but you can end in prison.

This is not like USA were you shoot anyone who enters in your property.

If you harm this people you surely will have to face penal consequences.

Why? Because then, people will do the same with a small family which can not pay rent this month, after you increased the price to the double because you want to rent to tourists.

The solution is simple: use your properties. Would you let your car with the keys inside? No. Don't let your houses unused. It's is an offense to people who want to work and live. Properties shouldn't be a business nor a speculative means.