I haven't redone paint on a sewing machine, but I know about paint on cars. It probably depends on what is causing the bubbling. If it's rust, it will need to be seen to or it will spread. If it was caused my heat exposure, its probably harmless. Here in the "sauna of the south" humidity related problems with paint are common. For me, if the price was right, I'd probably take the chance, but I wouldn't pay a lot of money for it.