There’s an interesting use of 業者 in the first few pages of this chapter.
p74
うちの仔すばらっしこすぎて業者さんに匙投げられて
I first completely misread this sentence as - our cat is so nimble that the delivery man threw a spoon at it…
After realising that 匙を投げる is a set phrase meaning - to give up (something as hopeless) or to throw in the towel - the sentence actually means:
Our cat is too nimble so the other people we asked gave up (trying to catch it)
業者 usually means trader/delivery person/business person, although can also mean “fellow trader”, or “people in the same trade”. So I think here it’s carrying a sense of “the other professionals we approached”, or “your fellow professionals”.
It comes again used similar further down the page by the guy with the spiders.