If you say the jeans are worth 5 cents and the fair market value is actually $120, yes, they can say that. If the fair market value is $5 and that's what you claim, that's that.
The reason there's a barter tax is that a lot of tax could be avoided by bartering. The small stuff is innocuous, but think about larger and more valuable things. "Fair market value" for junk is very low; "fair market value" for a house might be substantial. Of course, I agree that no one pays the tax. I certainly never have.
So the law seems pretty stupid then eh?
How much bartering for homes do you see going on? Was this a huge problem at one time? People bartering their homes for a can of peaches and the government stepping in and saying " NO" you can't sell that house for what you want, you have to sell it for what WE want!!
PS there is no sales tax on a home purchase. Box dwellers on the second or third floor may not know this.
The tax isn't the problem, they don't tax you for it, they add it to your income and you pay the tax on the house as if it were actual income and not a can of peaches. then you get to pay the $60,000 of income tax on the average home you just sold for a can of peaches. But since you only have a can of peaches and no money, looks like debtors prison for you ( It doesn't actually exist, its called failure to pay taxes prison now).