[SALChamps03]

What happens when the provider of the service spends what money s/he assigns him/herself?...Will they have to pay tax then or will the purchaser of their service pay their sales taxes for them too?...

They then pay the same tax that everyone else will pay. They are not being double taxed. One person pays a tax for the purchase of their services, and then they pay tax on the purchase of other goods and services.

[lewislynn]

They are not being double taxed. One person pays a tax for the purchase of their services, and then they pay tax on the purchase of other goods and services.

So they would have to increase the price by the amount of the tax then.