Be very careful, please! There is a LOT to know about how these work!
The home owner can sell anytime prior to the sheriff's sale. It's still their house. I'm new and feeling my way on this, so be aware! :-)
I'm looking at a house now that has no mortgage. I've found several of those, surprisingly. Don't know why people don't sell rather than risk a bid at sheriff's sale that just pays the taxes and costs...leaving them nothing. I guess maybe denial plays a part? In this case, they did not show up at court or file any answer. The house is quite nice, and appears to be occupied. The sale is coming up pretty quickly. An offer of 70% (less repair and holding costs) should net them a decent amount of cash after the taxes and costs are paid. Their alternative is to let it go to sheriff's sale and take their chances. Looks to be in very good condition, and is in a nice area, so not anticipating high repair costs. I just found it this afternoon, so letter going out tomorrow. We'll see. (I pretty much try to screen for free and clear or very high equity. The court recorder's office can tell you what liens, mtgs, etc have been recorded on a property.)
My caution to you, again, learn everything about how tax liens work. I'm still learning, and I've read a lot. Be extremely careful! Personally, I would never bid at auction. Purchase prior to auction, with inspection and title search done is the only way of purchasing that I would consider safe. I'm a strong believer in failure avoidance! One bad buy can wipe out the profit from your good buys. (Learned that lesson from antique auctions. lol)