Hi Ralph. I'm not too sure what your question is. If you mean as opposed to public land it is hard to compare one to the other as it depends on the past uses of the land and who went there. As far as public land goes it could be a forest or just wide open plains that nobody went to very much or a widely visited park. Private land can also vary widely like a huge farm or a small urban lot. The farm could be loaded with bullets, coins, artifacts or could be devoid of anything. Similarly, a small urban lot could be loaded with trash or it could have good finds. Private land is more apt to contain stuff as it is more unlikely to have been searched in the past unlike a public park that many may have searched. One doesn't always know until one tries and it can be one big find nobody was expecting or a big let down. Who knows as we can research a place for probability, but there's no certainty and it's possible to even overlook a good find as well.
I've been detecting some at a private Scout camp, established in 1949. My deal with them, was to "donate" all Scouting related items for their display cabinet, and I get to keep any coins or jewelry I fiind there. So far, I've given them about a dozen old pins and award items, and kept two silver jewelry pieces (and plenty of clad). Guessing that detectorists before me beat me to the older coins..
If you make a deal with the landowner, I suggest that you set aside any interesting items that you want to keep, then show the owner all the rest.