I recently became certified in checking for shatnez. I am wondering what is the based way al pi Choshen Mishpat to charge for garments. Rav Moshe writes in Igros Moshe Y:D 1:72 that even garments that are not 100% obligated to check for shatnez, the custom is to check for them. I am obligated to inform someone if their item halachically doesn’t require checking and if they want me to check it, I’ll check it? I don’t know everyone who drops of garments and whether they would want to be machmir like Rav Moshe. What’s the best way to go about it? It’s more of a service for my community. I’m not going to make it to the next tax bracket through shatnez testing.
I think you should inform them and that is what I did I believe when I checked decades ago. Most people don’t want to check what doesn’t need checking.