Alluding that services are not subject to sales tax is misleading. The state makes that determination, and some services are often subject to sales tax in some states.
Venmo is no different than other payment solutions, when you record the transaction in QB your record the sale with the amount subject to sales tax and let QB calculate the sales tax to get the total.
While automation is a wonderful theory, in application it falls short. Until such time as QB get a sales tax included function, download entries cause problems. Sales tax included would mean that you set the sales tax rate, enter the total amount and QB backs out the sales tax, posting retail sales and sales tax payable automatically.