How many times can you torque bolts on a hitch?

Technically if the bolts have never been over stressed it is ok to reuse them. The problem comes in not knowing how tight the original installer tightened them. Did he use a torque wrench? Or did he follow the rule of if tight is good then tighter is better, and standing on it is great.

For the costs of that few bolts I would also replace with new grade 8 bolts.