Tax lien auctions are risky ventures.
The county sells you the tax lien at an auction starting with the amount of taxes owed. The owner
has one year to pay the taxes plus interest (sometimes as high as 18%).
What almost every bidder would like is to get the tax lien at cost (that is exactly at the taxes owed) and for the
owner to pay up at the end of the year with interest=18%, so they make 18% on the money.
What ususally happens is that :
1) the auction gets bid up so that you make very little over what you would make in investments which are relatively safer, or
2) there is something wrong with the property that makes it hard to sell, so the owner is just walking away from it, and
you end up owning it when you had not intended to (and maybe you have to let it go for the taxes).
Since you actually want the property and these are bare lots, that is better. At worst, the prce is low enough that
you end up getting some decent interest, at best, you get the land (hopefully cheaply).
The fact that the lots are bare avoids the issues of evicting someone if they don't pay, since that can be an involved
and expensive process.