I have been doing research and see that either a designer charges based on an hourly rate or a % of the over all budget.

A rental property is like a work truck.

I recently bought a house to flip, and it turns out it will cost much more to renovate than I'd budgeted.

They serve as a good extension of your branding.Car and truck wraps generate more calls.  

You may not know how to handle: tenant relations, maintenance requests, contractors, turnover, lease admin, property managers, "professional" tenants, neighbors, capital expenditures, municipal codes, federal laws, evictions, lawyers, budgets, taxes, etc. and how each one can affect the profits (or eliminate them.)

Are separate meters included in your renovation budget?  

I have already asked my agent to ask the management of the building about the cracks and plan/budget to fix them.

Make sure you budget for more "Expensive" repairs.

He has only been seen driver the tenant's ex-husband's truck. 

I have a truck payment, and two mortages, one mortage is currently renting and Im making $350 a month profit off of it...So really I have my Primary mortgage, and my truck payment.My plan was to pay off that rental and then receive 100% of the profits every month, minus taxes and insurance.