However your buyer will likely want to get it tested and possibly insured to cover any leaks and resulting contamination.

As much as I dislike insurance companies, I have to agree with the ruling, poor or contaminated materials is not a covered peril, pretty clear that this is a product liability issue.

most sellers are reluctant to allow sampling for fear they will be in worst condition if the buyer finds contamination and then walks. the other question is are you going to finance the acquisition?

For instance imagine if the site has some environmental contaminants below grade.

Possible Title V and ground water contamination issues, may need a new foundation.

Every Google answer I found was it shouldn’t be done because it can contaminate the soils and groundwater.

If the dwelling has been damaged and needs repairs that most of the buildings seem like they need.. sheetrock, flooring,insulation, wiring,  due from water damage,, which was contaminated water.. they need to also comply and give tenants notice to vacate or be fined if they don't comply.. 

Even worse, what if your well becomes contaminated?

You have to bring suit to find out.For those that recall the environmental contamination days banks or lenders faced, they didn't want to touch the collateral until after the laws changed relieving them of clean-up obligations.

The sale price may not account for things like hidden title defects and/or liens, chemical contamination in the soils, foundations needing multiple piers sunk into bed rock, hidden damage in the walls from termites, one street over from the "War zone" side of town, etc.