Kaubi Mart means: Mart from Kaubi farm (Kaubi talu). We has not family names, only place name, like ancient creecs and indians :)
If slavery were liquidated (1816), the landlords put to the estonians the family names, usualy farm names.
Kaubi = kaup = 1. goods 2. product 3. commodity 4. item 5. merchandise 6. article 7. bargain 8. ware
And "Kaupmees" = "kaup + mees" = "merchandise + man" = merchant
Kaubi talu = "farm of merchant"
Often, children were of the same name as the old dad, grandfather = Mart, Jüri, again Mart, and again Jüri and so on. I think, that it is because old faith = with name is power and property. With name grandfather give power and property to children. Magic transmission of power. Farm or land was very imoprtant - life.