Rescue dog hates having his nails trimmed

I used to take my dog to get his nails trimmed but the woman who trimmed his nails moved and everyone else is too rough with him for my liking and his. I'm trying to do exposure therapy with him to the nail filer but nothing I do seems to be working. Treats, calming environments, just having him place his paw on top to feel the vibrations is fine but the actual filing he freaks. Any advice?