I am a LA'er and I would not have a business if I treated my customers like that. I may encourage the client to change there mind about something and warn them if I think they are making a mistake but it is up to them. If they bring there own batting I don't care but I am picky about thread and can usually talk the out of their thread because as she told you machines have a mind of there own and some threads don't run well on all machines.