Recently sold vacant land price info: not on MLS

[Mitra Samon]

Hi BP forum, thanks in advance for your help! I am looking to purchase a vacant lot within a community. Earlier in 2018, a nearly identical lot (next to next property on the same street) sold by original developer of the subdivision and I guess because it was not listed on MLS, the transaction info is not present there. I searched around online (nothing on zillow, Trulia, propertyshark, Redfin) and the only place there is info on the transaction on RealQuest.com (date, amount sold for). But, because it states the sold price as 75% of listed price (I know the listed because I had enquired about it back in Feb), I'm not sure whether to believe it. This is high-end lake-front property and knowing what this particular property sold for is invaluable to me since the one i'm looking to purchase belongs to the same developer. It's an ideal comp. How reliable is the info on RealQuest likely to be? Are there public records or any other sources I could look into? I'm not working with a realtor since I have lived in the area for 10 yrs and like to hunt for properties on my own. Appreciate your time and expertise!