All registered german .top domains got sold (by the registry) when they got registered - in other words, the registrant was the buyer and the registry the seller and the registration process was the purchase = sale.
Examples:
zahn.top (tooth)
brille.top (glasses)
adresse.top (address)
sportwette.top (sportsbet)
preis.top (price)
….. (...)
So the first german .top domain sales happend with the registration of them.
Now those, who registered them have the chance to (re)sell them, then there are again sales.
There are big german websites who use their name as .top - domain as forwarding domain, here are some examples:
gelbeseiten.top
otto.top
vorsorge.top
….. (…)
So, logically, the more german .top domains you own, the higher the chances that you will make a sale.
The better the keywords, the better.
As it is not possible to top a .top domain, there are top chances to make profit - although I don't knowww how long it can take, patience is required.