A lot or two," if vacant, contains uncertainty that most REI are unwilling to take on! 

Even small, common mistakes like renting below market, picking the wrong tenants, unwilling/unable to enforce lease terms, slow turnovers, or unscrupulous contractors can cost more than a good PM will charge, and that's before you account for your time and the stress.If you have the personality, I recommend self-management for anyone who lives within 1-2 hours of their investments.

Although I have great relationships with my main contractor (handling 6 units), he is unwilling to travel a bit further to handle some of the others. 

A pet fee or rent may give someone the impression that "they already paid for the damage" so they're unwilling to prevent it. 

We had factored the cost of the repair into our original offering price and the seller was unwilling to negotiate further.

If they are unwilling, terminate their lease.

If the PM is unable/unwilling to collect from the tenant, demand they compensate you for allowing the expense to occur.

I feel like lots of investors lose opportunities because they're unwilling to go outside their neighborhood.In terms of hiring a property management company, I think there's less risk since it's not your first investment property.

In the end, they were unwilling to do the loan, (cash out refi on a fifth mortgage) and I'd have been out the $450 if I'd have let her.

To get what you don't have in life you have to do what others are unwilling to do.