oil-that is dripping after installation of cat converter-say not their fault–things just happen
It is hard to imagine how they could have caused an oil leak doing exhaust repair, unless they did it…(cue dramatic music)
Normally a converter would have nothing to do with an oil leak. The exception might be if the converter was part of a header pipe that ran up near the engine and an oil pressure switch was inadvertently bumped, causing it to leak. Maybe.
Some more info might help make a wild guess at this. What kind of car, engine, how many miles, etc.?
Are you going based purely on the sound here or do you actually see the oil? Because new exhaust components, especially cat and A pipe, are notorious for making little pinging noises that sound exactly like oil dripping on them - - it’s actually just the metal contracting and is harmless.