HUD performed extensive due diligence on us, and had to approve us as buyer's and our management company and mangers.

I was hoping that the tenant would reach out wanting to negotiate, since I only really want him out and don't think I'll actually get money from him. 

And, past performance is no guarantee of future results. 

Or are they performing some sort of arbitrage and they are not the end buyer.

Put together a spreadsheet and compare the performance of the subject property if you keep renting it as is for the next 10 or 20 years versus if you rehab and refinance.

I only have good words about it, and cash flow is always over 100€/month per property.

That said, I’ve found that properties in C-class neighborhoods tend to perform best with Section 8 tenants.

I can only speak to the Texas market, where malls that focus on creating consumer experiences (coffee shops, kids play area, entertainment-based tenants) are still performing well even in this age of online shopping.  

Not sure why that happen, however the best way to screen a potential tenant is to see how they have performed in the past. 

If I only invested in REIT's or stocks 5 years ago when I started, my net worth would be 95% lower than it is today.