Tax does indeed tend to be a hard problem in these kinds of systems, but I think you (and most responses so far to your comment) are looking at it from the wrong end. It's the seller, not the buyer, that has to deal with taxes in most jurisdictions. For podcasts I'd expect the podcaster to be the seller and the listener to be the buyer.

Simplest example is the EU. When you sell a digital good to someone in the EU VAT is owed on that in the country in which the buyer resides, but the seller is responsible for collecting that VAT and then reporting and remitting it to the buyer's country.

The EU makes this simple. You can register with any EU country, and then report and remit you VAT for all EU countries to that one country's tax agency. That country's tax agency will then settle with the others. Ireland is a good EU country for this if you are a seller in a non-EU English speaking place. It takes about 10 minutes to register with Ireland online for this, and the quarterly tax filings with them are a simple CSV upload that you can also do in a few minutes.

Note that this means the seller has to know how much they sold to buyers in each EU country each quarter. That necessitates some form of tracking.

The situation is similar, but more work to deal with, in the US with sales tax and use tax. For sake of this discussion I'm just going to call both of those sales taxes [1].

It's more work in the US because (1) thresholds for taxability are often of the form "N transaction or $X in sales" usually with N = 200 so you can get above the threshold on a very tiny sales amount as opposed to EU where thresholds are based just on amount of sales, (2) sales tax is often the sum of statewide, countywide, citywide, and special taxing district sales taxes, so to actually figure out the tax on any given sale you need to know the full physical address of the buyer, and (3) while there is some cooperation among about half the states to do a system conceptually like the EU's, for the other half of the states if you meet their thresholds you need to register with, file with, and remit to each of them separately.

There is a way around this (besides just ignoring taxes). You can go through an intermediary that takes on legally the role of the seller. It is that intermediary that then needs to track how much is sold in each state and country and how much tax is owed.

That's how it works for app developers selling through the Apple app store for example. Until tax laws are changed to be more friendly to micropayments directly to content creators, going through some kind of store that aggregates content from multiple creators is probably the best we can legally do.

[1] A sales tax is a tax on the sale of something. A use tax is a tax on having something. The big difference is that a state makes the seller collect sales tax, but use tax is suppose to be dealt with be the person who owns the thing. It used to be that states could not force sellers to collect sales tax unless the seller had a presence in the state. So states would impose both a sales tax and a use tax, and the use tax was the exact same rate as the sales tax and had a deduction for the amount of sales tax paid. The net result was that if you bought something from an in-state seller they collected sales tax and you owed no use tax. If you bought something from an out-of-state seller, no sales tax was collected and you owed use tax on the full purchase price. If you travelled to another state, bought an item and paid sales tax to that state then brought the item home, and that other state's sales tax rate was lower than your state's use tax rate, you owed the difference in use tax.

The use tax exactly equalling the sales tax and being discounted by any sales tax already paid is because the Constitution restricts the states from regulating interstate commerce. Applying a higher tax to goods from out out of state than you do to domestic goods would run afoul of that. By making it so that the total sales + use tax was the same for imported and domestic item the state was not interfering with interstate commerce.

But a few years ago the Supreme Court overturned the cases that had said that states could not force sellers with no in-state presence to collect taxes. Now states can make out-of-state sellers collect the sales/use tax so for most purposes there is not much point in distinguishing between sales and use taxes.