Most likely they would just put the unpaid bill on your credit report and move on, leaving you with tarnished credit and no recourse.

The usual procedure about disputed debts applies.

Sure, and the credit bureaus will not side with you. Because you actually do owe the debt.

That is what they say. You say that the modem wasn't worth USD 500 when it was new and certainly isn't worth that much after five years of depreciation. In a civilized society, when two people disagree they go before the judge. If the judge says you owe the debt, then you do. If he says you do not, then you don't.

Can someone explain where the people defending iffy business practices are coming from? Has no one here rented from a shady landlord who tried to charge you $$$ for stains on the ten-year-old stained carpet that was already worthless when you moved in, and the practice didn't appear indefensible then?

The credit bureaus have sided with me every time I've made a dispute.

really? I did not even know this was a thing? do you have examples? can i pm?

And the procedure will ask them if you indeed owe them, find out that you do indeed owe them this amount, and uphold the debt.