I’ve been researching getting into buying properties at auction myself. I’m definitely not an expert but will share some of what I’ve learned. You'll really want to educate yourself first before making an actual purchase at auction. Some resources for that…
This website. A lot of great posts on here by folks with years’ of experience buying foreclosures.
The book Bidding to Buy. Great book that explains the process in clear simple terms.
The county recorder of deeds website where the properties are located. These sites are often FREE to browse and you can self-educate yourself on how to run a title search.
You’re already thinking on the right track asking which liens become unattached from a property. Generally speaking, liens that are in a senior position to the lien that’s held by the foreclosing party are going to remain attached to the property after it’s purchased at auction – liens that are junior are wiped out.
Government liens, i.e. IRS or local property tax liens are always going to be senior. Lien position is something you’ll likely want to master first, before buying at auction to avoid making a costly mistake.
Once you understand lien position, in order to determine which liens are senior and which are junior for a particular property, you’d have to either do a DIY title search on the county recorder OR pay a title company to do so. With being new to this I’d pay a title company for your first purchase.
I've attended a handful of auctions to get more familiar with the process, and at one I saw a couple pay $13,000 for what they thought was a 2 bedroom condo worth about $50,000. I'd looked up the liens when I got home and they'd purchased a junior lien… the HOA was the foreclosing party, foreclosing for money past due to them. If the couple still wanted the property when they learned this, they'd have to pay off the outstanding first position mortgage as well, which was in the ballpark of $40,000.
Good luck with it.
Rob