You're worrying over nothing. The refrigerant a shop uses is likely BETTER than most of the stuff you buy at an auto parts store. Pretty much every one of those DIY recharge kits has some gimmicky additive in the refrigerant that claims to do different stuff, like cool better somehow. Or has stop leak, or seal conditioners, or something else that can do more harm than good. I'm skeptical of those additives and would much rather have plain, pure refrigerant with nothing else added to it. And that's most likely what a shop would use. They buy large 30 lb cans of it, and those never have any gimmicky additives in them. You CAN buy regular refrigerant in 12 oz cans with no additives (which is what I use) at the parts store, but they're not part of a "kit" that includes the charging hose or gauge; it's just a can of refrigerant.
Don't assume you're low on refrigerant. There are a lot of things that can make an AC system stop working. Don't just blindly add refrigerant, hoping that it makes the problem go away. Diagnose the problem first. IF the problem is low refrigerant, find out where/how it leaked out. Then fix the leak (which will probably require you to evacuate the rest of the refrigerant from the system). Then vacuum the system with a vacuum pump to remove all the air from the system. THEN you can finally add refrigerant!