As a mechanic with a lot of experience on Cessna's, 3 big things.
1) The plane isn't rigged to spin. Period. Unless there's something extreme like a broken rudder spring - that's a terrible rigging metric. Straight and level on a calm day is when you check rigging. Look at the ball, see what its doing. Look at the VSI, play with trim, etc. Not saying it doesn't indicate a rigging issue, but if spin characteristics are what your mechanic is chasing, they are going to mess up the plane's rigging doing so - guaranteed. It's more likely to end up being a weight and balance thing (as stall is the precise moment aerodynamics have the least impact on your plane).
2) At this point for how much has been messed with, if I personally were approaching the rigging of this plane, I'd spend a whole day or two to reset everything to nominal and get a performance baseline, from you, in flight - and adjust one control at a time to get it perfect. There are differences in flight between aileron imbalance and wing incidence, for example - and if your mechanic doesn't know them, get them to outsource to an IA or someone who does. If you have doubts about this person - don't let them touch your eccentrics - AKA FRIGGIN WING MOUNTS.