As others have alluded to
ChangFai ; if you have any doubts I would recommend caution, you would not be the original owner so the frame warranty will not transfer over to you.
I'd ask for clarification on a few things, including the area I have highlighted with an arrow in the picture you provided. It looks like a weld with a tiny hole at the end; that's often what would be done to repair a crack that had started. In one of your other pictures you can see 'Eulogy' on the top tube. Potentially that's what it started life as with an
integrated seat tube; when the crack started it was repaired and the frame was converted to a shorter traditional seat tube in effort to reduce the stress at the area where the frame had started to fail.
If my assumption turns out to be correct you are not buying an 'Effusion' but a 'Eulogy" that has been repaired and altered. As that frame was introduced in 2007 it's entirely possible that the repair may have been done a long time ago, along with the help of the alteration it may well last a long time; it looks like it has been done well. But; as the saying goes "caveat emptor"; yes I am basing my assumptions on a few photographs on a bike model that was before my time at Enigma; but I'd definitely be asking the seller for some clarification about its history.
If you do decide to walk away from this particular one I'd still have Enigma on my wish list as a brand; they have come a long way since 2006. Their '
signature' range which are made in Sussex are absolutely stunning; the craftsmanship is superb and in my opinion they have grown and evolved to now rival the very best I have seen from any of the high end 'titanium' and 'steel' frame builder's in the world 🌎