Hello Jeannine.freund
Thank you for your question. Basically, the Roomba should not leave any marks on the walls. However, it always depends on the circumstances. Some of our users also report that they use felt so that neither the robot nor the wall gets marks from use. This can be done to be on the safe side, but in most cases it is not necessary.
We wish you a lot of fun with your Roomba! :)
Your iRobot Team

no problems with our walls. Also there is a roomba setting which makes it go very gently near walls - this seems to work well

We have a high-gloss sideboard and are very positively surprised that it has hardly any visible scratches or marks on it since it has been in use for over 1 year. But it is difficult to say how it behaves on walls with colours.
The fact is that it drives gently into the wall because it recognises it and then reverses before turning. So there shouldn't really be any marks, but in the long term there might be wear if you have plaster on the walls, for example.