Drill and tap it. If necessary, drill to a larger size and use a thread insert. MOST of the time, it's on the customer, or the shop may discount it. Where is it my fault as a tech that it's corroded? I try as hard as I can to avoid breaking bolts, because that's not really fun work, but if it happens, I didn't build it (or design), I didn't buy it, and I didn't break it (the problem that it was coming apart for) but I can fix it! Honestly, if a shop doesn't want to pay a guy for work, something that's not really his fault, I wouldn't stay there very long! If it's my fault that the bolt broke, then I take the hit.