Yechiel Michel Epstein,
Translation:Arukh ha-Shulchan…
“ And as for the Gemara’s retort regarding the firstborn animal, know that in that instance the expert cannot be paid for his service, as the Mishnah states in Gemara Bechoros 28.1. In addition, Rashi seems to imply in Gemara Shabbos that an expert would not want to check the animal on the festival day in any case (as the work does not befit the holiness of the day) . According to this explanation, during the weekday the retort ‘Who says he has met a qualified expert?’ would not apply. See there in Tosfos further, and if you look into the matter you will find this answer acceptable. ”
