If we agree in a truly free society then collecting and monetizing metadata should be illegal. If we don't mind giving up that freedom then there's nothing wrong with companies creating a profile on you and tracking you no matter where you go and what you do. But the internet has spoken and we're gladly, albeit unknowingly, giving up any right of protection. I find it worrisome to think of what society will be like in another 50 years if nothing is done to curtail the fleecing of user data.
Also, it doesn't matter that there's an exchange happening. Sales tax and income tax are assessed on fair exchanges of goods, services, and currency.
And if you grow oranges on your property that you never sell, you never pay taxes on those oranges.
If you accept a trade-in on the sale of a vehicle, the allowance for the trade-in cannot be excluded from the amount on which tax is based.
For example, if you sell a car for $20,000 and accept a trade-in valued at $4,000 as partial payment, tax is based on the $20,000 selling price.
Still though, the example is a good one. You're trading your data for a service. There isn't anything to tax.
In any situation, potentially derived value is not taxable. A car is worth whatever a car was bought/sold for, not including some hypothetical such as whatever I could make by driving it for Uber/Lyft. What matter's here is what will actually occur in the transaction. If Equifax chooses to sell its data, that income will be taxed at whatever price Equifax chooses to sell the data.
Note this doesn't change that your "gift" of peanuts of data is not taxable because (a) your data alone isn't worth squat, (b) even if it was, you got something in exchange for it.