This is a difficult question to answer because the majority of proper servicing goes-on inside the covers of your machine where you can’t see it. We recommend you try to talk to the service engineer before you hand it over – if he/she is negative about servicing your machine, find someone else! Following a professional service, your machine should sew correctly in all the modes and patterns it is supposed to and really, you ought to notice a significant improvement in the way it sounds, feels, and sews than before you sent it for service. Your machine should come back with a comprehensive sew-off sample showing a comprehensive set of its stitches. If you are at all unhappy about your machine after getting it back, don’t hesitate to take the matter up with the service engineer.