These places can still appreciate and you can check each city's popuplation growth or decline on https://worldpopulationreview.com/.  

I asked them to pay 2 months deposit so I may get more surety, but they declined saying they cannot afford it.

If the latter, people have tightened there wallets and certain areas are seeing a decline.

With these declining commercial spaces, these communities could be at risk for blight.If you look around, you will see new retail spaces.

Lenders have been accommodative for the last couple of years because they were facing a declining market with no buyers. 

Booking.com fidnt blink at my decline now 3 weeks later, they tried to cancel again claiming their dates change and they couldn't make it.

Go where the population is growing 5-10% per year (even though it is a small denominator) over chasing year 1 cash flow in a stagnant/declining market.

Duluth has traditionally had a strong college rental market and thankfully any small decline in enrollment rates haven't been as severe as other traditional college cities, eg.

As far as rates I see them declining slower than expected but lowering nonetheless. 

You’re not required to rent to someone just because they look great on paper, but you should ensure that your reasons for declining them are grounded in business-related concerns (e.g., concerns over rental history or ability to care for the property, if documented).A good practice is to follow a consistent screening process for all applicants.