This is more of an issue in warmer climates where AC is used often. Many things can be used as a refrigerant. In fact, one of the best refrigerants is propane. Remember that it's really the pressure-temperature relationship that's at the heart of
your AC system operation. Different applications use different refrigerants. Your home AC system does not use the same refrigerant as your car or your refrigerator. That doesn't stop some people from trying to put these other products into their automotive AC system.
The bottom line on this is that it's a big no-no. Mixing refrigerants is dangerous and can cause big problems in your AC system. In fact, if you have a contaminated system, some shops might not even be able to work on your vehicle. This contaminated refrigerant has to be handled separately from your regular supply of refrigerant, and as a result, it makes it very difficult to recover.
Many professional refrigerant recovery machines come with refrigerant identifiers to detect the type of refrigerant in a particular system. If they find contaminated refrigerant in your vehicle’s AC system, they might not be able to service your vehicle. Don't mix refrigerants, and if your system is found to be contaminated, you might not be able to have it serviced at all. If you weren’t the person who installed the contaminated refrigerant, perhaps the last shop that served your vehicle did. You might have some legal recourse, but that would be up to your local laws and regulations. The best way to avoid this issue is by dealing with reputable shops that have professionally certified AC technicians.