Whoever comes out on top has to report income, and whoever comes out on bottom has to report the expense.
Seems like the tax rules outlaw pure barter and make you use dollars in your transaction whether you want to or not.
This is part of what it means to be a national currency -- it's what the government accepts for payment of taxes.
I mention this because you specifically call out "equivalent value to the traders".
That value is not something you can tax directly. It's more like happiness than cash. In the barter, the traders walk away with the same value of goods, but greater happiness. I'm not sure what dollar value the IRS places on happiness, but based on their behavior, I'm pretty sure it is $0 per smile.
Therefore, neither trader in a normal barter should realize a taxable gain.
In a happy coincidence for the IRS, assigning monetary values to everything makes it trivial to assign a value to the trade for the gaining party to pay tax on. Again, not relevant to what barter is.
As you say, anyone with enough cash available would always prefer settling with two trades using money instead of one barter trade. So really, the barter tax is only levied on people who don't have the money to pay it and on tax avoiders. The tax avoiders find another loophole; the poor people remain screwed.
If the barter is an exchange of goods for services (I'll do your taxes in return for 10 dozen eggs from your farm), then the party that received the goods in exchange for their services owes income tax on the fair market value of the service provided. The party that provided the goods would owe income tax on the capital gain of the goods (fair market value minus the cost paid, or basis).
If both parties are exchanging goods, then it gets more complicated. In some cases (I trade you the deed for my apartment in the city for the deed for your beach house), the IRS deems it a "like-kind exchange", which is NOT a taxable event -- the basis of the old items carries over to the new properties. However, if I exchange my apartment for your car, then it's not a like-kind exchange, because the items exchanged are not of like kind (makes sense?), and both parties pay capital gains (or can claim a loss) vs. the fair market value of the exchange.
To add to the fun, one can do a delayed like-kind exchange by storing the proceeds with a "qualified intermediary", a form of escrow agent. This is often done with real estate, since it means that the counterparties don't have to be willing to swap deeds. To give a specific example, I could sell my apartment in the city, deliver the proceeds to a qualified intermediary, and use them later to buy a beach house, and it would be treated as a tax-free exchange by the IRS (if the prices of the two properties are equal and some other criteria are met).
>> However, if I exchange my apartment for your car, then it's not a like-kind exchange, because the items exchanged are not of like kind (makes sense?), and both parties pay capital gains (or can claim a loss) vs. the fair market value of the exchange.
You probably can't claim a capital loss for a car as you can only claim it for things you hold for investment purposes. Since the car's depreciation is expected to be because of personal use you can't claim loss on it whereas if it were to increase for some reason (memorabilia) you'd have to pay gains.