I find that less annoying then trade spam to be honest,
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I suspect it actually introduces a absurd amount of gold into the economy though in a round about way. Those hundreds of bots you see in low dungeons (still mostly tbc ones and I admit I am unsure why... I think vendor value?) Tell their items to buy and sell tokens as well as selling blizzard game keys as third parties via the gift system.
I don't believe they add as much gold as the WoD garrison for a benchmark but it likely is at least comparable.
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A pretty fair amount of people boost. I am a part of a few discord servers and have an extremely high raider and pvp raiding so outside of level boosting I have access to each post looking for carries. This is only for NA I have no information on EU
The most popular big communities get roughly 2-3 thousand boost requests a week for pve content. With smaller ones like getting 300-500 though the prices remain more or less identical.
PvP boosting is almost always a 1 on 1 negotiation with a whale and prices range wildly the only streamlined version of pvp boosting is 1800.
I would hazard an educated guess that roughly five thousands boosts are bought every week in wow with the most popular run being bought a mythic 14. Most people buying boosts are BR players and without going through more then a hundred orders it looks to be roughly at a 2/3 breakdown between them and na players.
How many of those are token sales is something that I can only speculate on but given the condition of the characters being boosted alongside them almost uniformly having no time invested in the character I would hazard a guess the vast lionshare buys tokens.
With all that said if it was pushed underground by blizzard and hidden away I doubt anyone would care all that much. The issue is its in everyone's face constantly.