Wedge pointed out that Vavle would get part of Badspot's income from Blockland if this happened. It's for this reason I'm not sure this is such a good idea. Out of every 20$ spent on a Blockland key, Badpsot only gets like 3 of those dollars because his income is already split up among not only the government for taxes but also Garage Games. Mix Vavle up in all that and Badspot is getting very little money out of his game, and if Blockland isn't financially successful enough on Steam Badspot could be losing a lot of money.
Taxes don't apply to the purchases.
Badspot makes $10 off each key, at least that was what I remember from an old discussion. The other $10 goes to Garage Games. VALVe would probably take $5 of that $10, but Blockland's popularity would increase giving Badspot a greater income.