1. Quality of the vacuum coating
Obviously, this will be the most important factor as far as determining which company you will be going with. You need to determine if the vacuum coating the company is providing is worth the money they are charging for it. Do not make the mistake of thinking that vacuum coatings are all alike. The processes that companies use to create their vacuum coatings are very different. Therefore, this has a direct impact on the durability of the coatings. Ask for a few sample items that have already had the vacuum coating applied to them. Put these objects through a series of tests of your own design. This will help you to figure out if the coating is strong enough to handle the abuse that the objects you will have coated will be subjected to.
2. How long will the process take?
You do not want to wait around endlessly for your vacuum coating to be completed. This is why you must verify the expected turnaround time for any company you are thinking about hiring. Finding a company that provides excellent quality vacuum coating will not matter if it takes them a long time to finish their work.
3. High volume purchases
Will you be needing vacuum coating for a large number of objects for the foreseeable future? If this is the case, you should inquire with the companies you talk to about the possibility of getting a discount since you will be placing so many large orders. It is not unheard of for vacuum coating companies to lower the usual rates they charge for customers who will be placing an extremely high number of orders.