I have been to several county tax sale auctions. In Utah, they usually happen in May. I have bid on at least a dozen properties over a 5-year span. I have only purchased 2 properties - both land deals. One was an orphaned easement next to my sisters old home in Provo, UT. It was about 10 ft. wide by 60 ft. deep. I'm sure it only had value to the 3 contingent property owners. I think I got it for just under $1,000 and it was a great buy to add value to their existing property. Most tax sale parcels in good areas are like this. They are weird shapes and not build-able or left-over from something years ago and land-locked. After being named as the high bidder at the auction, you have about 2 hours to pay the full price in cash.
Another property I purchased just last year was 118 Acres of raw land in a rural area 2 hours east of Salt lake. The bidding started at about $8K as I recall, as that was the delinquent tax amount. I was the highest bidder at $30K and I had brought the right configuration of cashier's checks to close just after the auction. I had to go through a "quiet title action" with a local attorney to be able to guarantee free and clear title to the next buyer. This took 3 months and cost $2,200. I had a local agent list the property at 139K and we had some good interest but the only real offers came in quite low. We sold after some negotiation with the property owners next door for 95K and netted about $56K after all commissions and fees. From purchase to sale it was about 7 months. I attended the same auction this year, trying to do the same thing but all the best properties were "redeemed" (taxes paid) or simply sold too high to make sense to me.
It makes a great story but I'm not sure it's predictably repeatable. Another play is to get the county delinquency list as soon as it comes out (usually 3-5 weeks before the auction) and try to make contact directly with the delinquent owner. If the land is worth 50K and the delinquent taxes are 7K, the owner might be willing to sell for 10K over the tax amount and you get a bargain!
To get started in Utah, I would suggest you google the counties you are interested in, and the key words, "delinquent tax sale" and the current year. Do this next April in 2019. Find the property lists and auction dates and make sure to do your research on the properties that make sense. Know what you are buying and DO NOT OVERPAY!
Have fun out there! It's kind of like a treasure hunt!