A tax on the value of the transferred item, or tax on the $20 or so he charges to perform the service of transferring? The former would depend on individual state law, the latter on how the guy does his own accounting.
Amazon and other online retailers have a different set of hoops to jump through. There is also the practical matter of what the tax code says, vs how it is enforced. You buying a single small item from an online retailer is probably not worth the state's time (yet, wait until the relative newness of e-commerce wears off, the local tax take falls too much, and database software improves), large items might not be. Cars, boats, firearms, etc all have a lot of accompanying paperwork that would make it easier to cross-reference the tax information. Some of the anti-gun groups target any technical errors in complying with law to advance their agenda - I found a few while googling this topic.
This neatly falls under the topic that tax code is hopelessly complex, and those like the Kerrys can afford an army of accountants and lawyers to run rings around the po' folk.
http://www.myflorida.com/dor/consumer/
Here in Colorado, except in Denver which is a special screwup, we dilligently pay the state a use tax on out-of-state purchases except in the instance where merchandise happens to fall into a lake