When your commercial appliances need replacement parts, it's understandable that you'll do whatever you can to save money while still fixing the appliance. Replacing things yourself and finding cheaper generic parts may work in a pinch, but if at all possible, you want to go the more official route. Not only will the work carry a guarantee, but having repair companies do the work means you stand a better chance of getting manufacturer parts from suppliers with extensive inventories.
If you have older equipment, those appliances may no longer have warranties covering them. But for those items that do still have active warranties, always read the fine print to verify whether or not repairs you make invalidate the warranty. These generally don't include simple things, like changing a light bulb in a refrigerator or replacing a removable shelf. But if you do any other work on the appliance, that could end your warranty right then and there. If you see wording to that effect, you need to call a repair company to do any replacement work.
Know When to Have Parts Professionally Replaced
Before you get too deep into the inner workings of your appliances, know when to stop. There's a point where you know you have to call a repair company to have the replacement part installed, but a lot of people don't stop trying to install things themselves at that point; they push on for a bit. Learn to spot those things that you can't install yourself early on so you can put the appliance back together and wait for the repair company.
Go for Manufacturer Parts Whenever Possible
Your appliances were made to work optimally with specific parts made by the manufacturer. They'll work just fine with cheaper parts made by other companies, but for optimal life span and function, you want to use parts from the same manufacturer. These can be more expensive, and if your appliance is older, potentially harder to find. But appliance repair companies may have back stock, and the manufacturer may be able to recommend certain third-party brands if original parts are no longer available for the models you have.
You can always have an appliance repair company handle part replacement. They have access to wholesale parts suppliers who may have a bigger and more varied supply on hand. If you have older appliances, then you have a better chance of receiving the correct original part.
Contact a local commercial appliance replacement parts supplier to learn more.