My $.02:
1) $700 is low on the PITI part. Im thinking closer to $800. Taxes in TX are 3%, which is around $300 a month. Not sure what type of 'smoking finance' deal you are getting, but 5% amortized interest would be $430 for the PI part.
2) "Turnkey" does not usually mean: Need new roof. A roof, depending on the size of the house, can cost 10k+. Do you have any quotes on the roof by someone that does roofs?
3) Have YOU done your own due diligence to determine what rents are in the area? NEVER rely on a property manager for what you THINK it might rent for. Although it MAY rent for $1300 a month, it MAY also stay on the market awhile until that person comes by. A more realistic number could be $1100 (or even less) if you don't want to turn the property every year. I usually take the 'low' end of Zillow as I can find good tenants FAST that way. Then I 'boil' them like lobsters over time. ;-) My average stay is 4 years. :-) Turnover is a HUGE cost, especially if you have a property manager in the middle. :-(
4) If it needs a new coat of paint in the living room, it probably needs a new coat of paint EVERYWHERE. Budget $1000 for interior paint. ;-)
5) How old is the house? If it is over 20-30 years, your maintenance budget needs to be ready for all kinds of possibilities.
6) Property managers will USUALLY take your first months rent PLUS 10% of all rents received to place a new tenant. That will seriously cut into your 'profit'.
If it was me, I'd get a roof estimate and then renegotiate the price. IF all the other numbers you state are true, I'd move forward.
Alan