Can a debt collection agency sell your house/condo?

No , but they can force you into bankruptcy.

As a rule, they cannot sell what they do not own or for which they have no legal or equitable title.

If the debt collection agency bought the mortgage from a lender, they can foreclose. If the debt is unrelated to the mortgage or the property - such as credit card debt and unsecured loans - the collection agency can sue you for the debt and win a judgment against you. In some cases, they may be able to get a lien recorded against your property, but they can't foreclose on it/sell it. The lien just ensures that they get paid next in line after the mortgage lender, when you sell it.

they have to successfully sue you in Court, first ........................................

If the debt collection agency assumed your mortgage...sure. Its called a foreclosure.

They probably wont do that though, its easier to sue you.

No, and why would they? Their job is to collect a debt. If you owe a debt and you aren't paying it, you can be sued. When you lose the lawsuit and have a judgment against you, then a lien can be levied on your house or condo and then the house/condo can be foreclosed on. All a collection agency does is try to collect the debt, to avoid a lawsuit, which would be to your benefit, because you wouldn't have collection costs, court costs, interest, and foreclose proceedings costs added to your debt.

No. They can sue you and put a lien on it. But thats very, very rare.

No.

No. They can place a lien.

no .. but if you have unpaid back taxes your property is in extreme jeopardy ..