Thumbs up on the nitrogen test as this is best practices. We used a tank at the dealer. I have more tools and equipment than a man is allowed to own, but I have a small tank of nitrogen, 2 sets of gauges, regulator, tank of R134a, GM O-ring kit, in-line-filters (ACDelco), J-Tool line repair kit, PAG oil injector kit, 2 vacuum pumps and a refrigerant identifier (At home / Retired). Yea crazy, but I have a diff spreader also.
With a heavily regulated industry, shops with charge stations are equipped with identifier and the stuff sold in the aftermarket, cans of "Fix-It" juice contains nasty solvents designed to swell O-rings and seals, plus they contain ester oil. Ester oil will turn to acid when exposed to moisture if a leak occurs in the future. Some solvents will dissolve the desiccant bag in the accumulator. This juice will be flagged as contaminated every time if you go in for service at a licensed shop for future A/C repair. They have 3 tanks for cleaned, new or other (Contaminated). They have to pay to get rid of it. The can stuff will cause trouble.
The contaminated stuff will damage your HVAC and a shops equipment, thus a filter & identifier are mandatory. Use nitrogen and HVAC soap, fix what you have, vacuum leak check, replace lost PAG oil volume, install a good quality dye, then charge the system. Maybe I am too picky, but 30+ years of doing repairs from bumper to bumper, cutting corners will bite you every time.