Look at their bids. if they don't know the actual names of the items they plan to install or they don't use language like linear ft, square foot, depth, or know the proper name of materials like Trex, mosaic, service disconnect, hidden hangers, etc.

Sam you absolutely want to have an attorney draft proper documentation as sometimes rent to own can be construed as a mortgage and you would need to go through a foreclosure which is last thing you want to do.

Any suggestions on how to evaluate it vs a buildable lot with proper street access and utilities?

Well I will mention Proper @Greg Janes!

Can achieve high returns due to interest and penalties (8%-36% annually for tax liens).Can buy properties at 20%–60% of market value.Entry prices can be low, especially for tax liens.Lengthy Redemption Periods-You can face waiting periods (6 months–3 years) before taking possession Undisclosed liens, environmental issues, or structural problems can drastically increase costs.Auctions, especially online, can be competitive, reducing potential returns.Navigating county records, legal procedures, and filing paperwork can be challenging.structured education significantly improves outcomes, particularly avoiding mistakes.education helps with understanding local laws: processes vary widely by state and county.and proper due diligence: evaluating title reports, lien positions, and property conditions.and learning effective bidding strategies.Common Pitfalls without training can be miscalculating holding periods and returns.Overlooking hidden property or title issues.I cant recommend any training providers that I know about. 

Many basement foundation leaks can be addressed via:1) Proper gutters & downspout extensions2) Regrading around the foundation, so ground slopes AWAY from foundation3) Seal the driveway-foundation seem every year$20k sounds like an insane amount, would gget another 2 bids to compare.You don't seem to have enough evidence to prove the seller knew about the water issues.

To protect the 1031 status, they should hold the property for at least 1–2 years as an income-producing rental, report rental income on Schedule E, and document all activity properly.

They probably didn't have the infrastructure to underwrite properly, buy right, manage correctly, or even dispose of them correctly.  

That said, a properly used WY or DE LLC can be extremely useful, especially for real estate investors that own multiple properties and want to do so anonymously. 

Approximately 85% of the first year premium, in a properly-designed policy, goes to the cash value.