You don't need to pay someone.
For mechanical, take 1 small screw top jar, make a tiny hole in the centre of the lid, poke a piece of bare wire through the hole.
Now take the back off the watch, attach the watch to the wire so that it hangs above halfway in the jar. Fold the wire flat on the outside of the lid, and seal it off with insulating tape.
Into the bottom of the jar, pour in some solvent fluid like petrol/meths/paraffin, or anything stronger you can find.
Screw the lid back onto the jar. The watch must be clear of the liquid.
Leave for 2 - 14 days, and try the watch again.
For Grandfather clocks, you put an open container of solvent at the base of the clock, and then seal the clock completely. You maybe will have to wait a few weeks until it does its job.
Works for any size clocks, you just have use the most convenient system.
And for digital, take the battery out, and bung the watch in the fridge overnight.