The watch is original,what are your concerns?
It is genuine I believe. However the case plating is really worn out and it is not the most sought after Omega. If you like it go for it as it is not very expensive, but considering the model and condition it's not a particularly good deal neither.
Mostly the fact that he says he got it second hand and obviously has no box or papers and that the price is quite low or am I just over exaggurating. Also this is mu first time buying a watch from online auction.
You didn't get it all that cheap. It is a poor example of an unloved design which may cost £150-200 to get running right. The case damage can't really be improved.
As noted above, the watch is legit, but it's not particularly desirable and the condition is poor. It's actually quite rare to find an old watch that has the original box and/or paperwork.
