The difference is that once someone sells or buys there item, they stop spamming. The boosters don’t ever stop because they are selling an “infinite” service. Thus the result is that if you try to sell or buy something, you’re constantly drowned out.
I don’t know what it’s called… Premade raids for current raid tiers and then scroll through the list of people recruiting for raids. When you look for Ny’alotha heroic (for example), you’ll see like half of them being boosting services, which makes finding a legit run much, much harder.