Say you have mats and want an item crafted. You hand the mats over to someone that agreed to make an item for you. They decide they aren’t gonna do it and keep your materials. In this situation Blizzard can assist as crafting falls under the supported group and they just scammed you out of your materials for a service they were offering in game. Blizzard suspends them and returns the mats to the owner.
An unsupported transaction is when people agree in game or outside of game logs to provide a service like running you through 20 dungeons for a set amount of gold for example. You can pay them in advance like the op did and they could decide to quit carrying you after one dungeon and take your money. Now if Blizzard can prove with game logs that the agreed amount of runs was 20 and they only provided 1 then they can remove the gold from the offending player and maybe tac on a suspension for a scam.
But in this second situation you won’t get your gold back as Blizzard doesn’t provide power leveling services that are hosted by other players within their game worlds. You are making a deal with a stranger and not Blizzard entertainment. The first situation is a protected act as not everyone can be every type of crafter and those types of interactions are protected as they are normal parts of the game.
Paying for made up services is not.
It literally doesn’t matter if they say WTS in the chat. Just because they have a service to sell, doesn’t mean it’s a protected one.