You may have to renovate a property, building maintenance fee may go up, rent will come down and vacancies will rise as the old properties become undesirable with time.

If your rents get below market rent, it may never be possible to get the rent to market rate with the existing tenants.There is no better way to get rid of an undesired rent than to raise the rent above market rent and have them give you notice. 

Failing to do so may result in undesirable tenants and financial loss.Enhancements:Sometimes required due to market competition: For example, if all similar properties on the market have granite counters in the kitchen and your property has laminate, you may need to install granite to rent the property at market rate.Cost-justifiable enhancements: Changes that increase rent and have a reasonable payback period.The formula we use for estimating the payback period:Payback Months = (item cost) / (monthly savings or increased rent)For example, suppose the property has laminate kitchen counters.

The property needs some tlc which is why it's a good deal but the small things that need to be fixed have made it "undesirable" to the 2-3 carriers that are left in this area willing to write rental properties.

Ditto with the time and cost (possible evictions) of getting rid of undesirable tenants, not to mention the risk of additional unforeseen damages when unhappy tenants have to move out.Mom and pop owners are notorious for not counting expenses, not the least of which is their own labor and management.

A place where I see good money to be made is in houses that are undesirable because they are really weird but can be made unweird easily. 

-I'll have to screen out all the scammers and undesirable candidates (plan to avoid craigslist)-I'll have to show properties-candidates using a Realtor won't be able to contact me since I'm not a Realtor and don't want to be.

Even cash-flowing properties could be undesirable for a bank’s risk appetite for refinancing.

It is very rare for a mortgage company to miss out on protecting their first lien position by redeeming the unpaid taxes.That's why the tax deed sales are usually a waste of everyone's time - the good stuff is almost always redeemed and by the end of the auction, only the tax deeds secured by undesirable properties are left standing.

There could be very undesirable people such as child molesters or convicted felons staying on your property so I would at least want them to not have access to the part of the house my family stayed in.