It is necessary to ask the seller to show the documents certifying the ownership of the land plot and to provide the cadastral number of the plot. Among the documents certifying ownership of a plot of land can be a state act of ownership (issued in 1992-2012), a certificate (extract) of ownership of real estate (issued in 2013-2015) or an extract from the State Register of Property rights to real estate (issued for certification of ownership since 2016).
Using the cadastral number, you can find a plot on the public cadastral map. This can be done online - https://kadastr.live/#5/48.43/32.77. This is how you can find out if there is a plot of land at all, and where it is located.