Hoi Daniel, welcome to the FOG. I see from our link to marktplaats that you're from Holland just like me. I bought all my 5 Festools through marktplaats, some new and some used. You definitely have to go by in person and check the tool out yourself. It sure is also handy to read a lot about the tool on the net before you buy it so you know all it's in and outs before you buy it. But I guess you already got that part covered for, since you (also) found this website. There's a lot of info here about the Domino.
When dealing with people on marktplaats you have to make sure of a couple of things. Most people are good people there but there are also some crooks active on marktplaats. There is a very specific Festool con man active right now so be very aware you're not getting fooled and only deal in person. Seems the person you're dealing with is not that con man though, so no problem there. But what I had once for instance, is that I drove 2,5 hours on my bike in the rain to buy a used DS400 and when I got there I was presented with a machine that looked much worse than I could remember from the pictures. When I got back at home I checked the pictures from the ad I saved to my hard drive again and found I got a machine that was another one then on the pictures. So he put up a pic of a nice tool and tried to sell me a lesser tool when I got there.
The joke was on him tough. We originally agreed on a price of 80 euro. When I got there I was really disappointed and felt something was not right. But when you drive 2,5 hours through the rain and have to drive another 2,5 to get back, you don't want the trip to be for nothing. So I was contemplating to myself for a minute but in no way was I going to pay 80 for it. The guy saw me hesitating and suggested I'd buy it for less. We agreed on 40. Back home I completely cleaned and refurbished it and sold it with 60 euro profit. So I was lucky, but beware, because he was trying to fool me by putting fake pics up on marktplaats.