ask him what is included
what parts are replaced?
New torque converter?
Is the valve body updated?
New solenoids?
new front pump?
does he do any machine work if the case /valve body needs it?
With a auto trans on the table and taken apart there are two ways to put it back together....the quick cheap way with a road test and no valve body work
or
the re manufacture way where the whole trans is re manufactured from front to back and all updates are performed and installed
A "soft rebuild" with a 5r55e can be when the nightmare begins
get what you pay for
His parts cost for all parts to reman a 5r55e is anywhere from $400-600 so to think he is willing to only make $500 or so out the door with labor, new fluids and filter ....chances are he is not putting the full $600 worth of parts into that 5r55...more likely just identify its current issues, replace the soft wear items and put it back together. It is always best to ask some questions to make sure your $1200 is going in the right direction