You would likely only have a case if you could prove he knew about the problem, , and he knowingly lied. That is nearly impossible, unless you could find a garage who quoted in the last few weeks, for essential repairs to the bike, or something like that.
Then you'd have to take some sort of a civil case or something, alleging he deliberately mislead you, and 'robbed' you. Again this might not work.. you purchased a second hand bike, for approx 1,250. A cruiser bike sounds expensive enough, so not sure what condition a 1,250 Euro cruiser should be in.
If this was purchased from a garage what would be the difference? They can hardly have to stand over problems on second hand goods, unless they knew about them and covered them up. Some parts just fail, and it might not have been possible to predict this failure.
OP, do you mind stating the nature of the problem, and are you certain that the seller knew about it? For example, if the fuel pump failed it is unlikely he knew that was going to happen... on the other hand, if a repair was temporily patched, then that indicates someone knew about the problem,.. but perhaps not the seller.
Unfortunately I don't think you'll get any comeback here...