Dembele, 20, made the move from Dortmund to Barcelona for a reported €105 million late last month.
It was the La Liga giants' biggest signing of the transfer window, having needed desperately to try and replace Neymar after the Brazilian's world-record move to Paris Saint-Germain.
Rauball said Dortmund were clear with Barca from the outset, setting out what they wanted for the France international.
"In the case of Dembele, we didn't let Barcelona screw us and made all the conditions clear from the beginning," he said on Tuesday.
"If they hadn't met those conditions, the transfer wouldn't have been possible.
"The fact that it happened shortly before the window closed is just the way things are.
"Nevertheless, we really have to think about whether we can accept the fact that such transfers are possible until the end of August."
Dembele ended up spending just one campaign at Dortmund after joining from Rennes last year.