"Collections" doesn't result in you having to pay unless you are sued (by the landlord or the collections agency--it depends on whether the agency is working for the landlord [in which case the landlord would sue] or purchased the claim from the landlord [in which case the agency would sue]). If they feel the claim is justified, they could sue; and if they can prove in court that you owe the money, they can get a judgment ordering you to pay it. But they can't do anything like garnish wages, levy on a bank account, etc. without going to court--they need to sue you and win to take legal action.