Yes it is a genuine Sonor Swinger snare from the early 70's. There were a couple of versions, this one with a copy of the Ludwig Imperial lug. I think that was the earlier one, the later one which I have has a stubby looking bowtie lug. I'm almost 100% sure that the one you are looking at is a plastic lug as is the later one.
At some point they also changed the shell. The earlier one, like yours has the ridge around the middle, the later one is just a straight side. Both are seamed shells and I believe have a rollover bearing edge...at least mine is. That is something you might want to check. Throwoff and butt are good quality...actually the same as more expensive drums. Toward the end of the Swinger run they went with more inferior parts.
These were low end budget drums from Sonor and so the do not have the value of other Sonor products. I would say 90 Euro is too high for this snare. 50 Euro would be a reasonable price in my opinion. I got a complete set of Swinger drums with a mint snare for $100 US.