Here's the answer from my FFL.
Started with an audit in 1991 (pre Quill decision). At the audit, it was discovered he was accepting shipments from out of state FFLS or individuals and transferring them to residents of Florida without collecting the sales tax.
He paid the tax, penalties and interest. He, thereafter, collected tax.
Later, not sure what year, but after the Quill decision, a customer contacted the Department of Revenue and allegedly was told no tax should be collected.
Rather than simply taking the customer's word for the conversation with the Revenue folks (and, I guess, giving the gun to the cistomer without colecting the tax), the FFL called Revenue himself and talked at some length with a supervisor.
He was told that if the was transferring a firearm received from another state he HAD to collect the tax. And, he does.
He also has to pay income tax on the sale. He transfered a firearm worth, say 500 bucks. He collected the 7% tax so his transaction shows he sold a gun for $500.
He probably could back out such sales and not pay the income tax, but he said he does so few it is not worth the possibility of a tax hassle with the Feds and/or State.
Bob