most shops wont work on a ski after the 3rd drilling.
depends on the skis/placement of hole to determine how much the ski can really take. On most skis, the core will be pretty torn up after the third or fourth drilling. A few skis can handle 4 or 5 ok, but those are pretty much igneous, volkl explosivs or similar skis with metal under the topsheet, probably head m103...and a handleful of other skis.
assuming they are park skis, I would stop at the 3rd drilling