This fee compensates me for the extra work required for the unexpected turnover and to advertise and vet a new tenant.

A lot of unexpected can come up that you didn’t even think about.

Will you have enough money to cover unexpected costs? 

If you are 90% leveraged in a market with dropping values, you’re in a tough spot if you overpay and if you don’t have sufficient reserves to account for an unexpected HVAC replacement or a tenant who stops paying/vacancy.  

My tenants that enter the house in May were paying okay, but in September they start paying late and in October they asked me to pay a partial amount because they had car accident and he in the hospital and I accepted, but now in November they asked me again to do a partial payment even they have not pay the second part of October, so this time I told them that I will not accept partial payments anymore and they have not pay, so I sent them a 5-day notice to pay or quit, and they sent me yesterday a message saying something like "we just asking for few more days to pay, but if you evict us our attorney will reset the eviction and it will take you like 2 months to get the house back", so I am not sure what to do.

It's essential to have contingency plans in place for unexpected issues that may arise during the renovation process.

Things happen that have nothing to do with market factors...and you may end up needing to exit some of your investments unexpectedly sooner than you originally planned.  

I'm curious, what are some things that have come as an unexpected benefit to folks who have a few deals under their belt?

I miscalculated the renovation costs; ran into unexpected expenses (e.g., the stormwater and sewer lines were combined so I had several sewer backups and had a lot of push-back from the municipality before I could redirect stormwater into the street); Contractors didn't show up which gives subsequent contractors with a great excuse for them to not show up (i.e., the domino effect thing).In summary, don't partner with anyone, borrow money from a HML or preferably from your uncle Billy to get you through construction and then refinance it through the VA.

My first purchase was by accident.