With a bit of luck you should be able to sort out any minor issues your self by go through a list of check points before handing it in some where; Needle in the right way (so easy to get wrong when it's been a while, or you go from one machine to another); same for threading the needle, either from left to right, or right to left (theres' a recent thread on this particular issue with model 15). Then double check threading in general and cleaning feed dogs, bobbin area, behind the face plate and under the base. Check that the bobbin is evenly wound, and bobbin thread goes in the tension spring the right way (I don't think it's possible to get it wrong on the 15 though). You should certainly not give it up :- )