No need to apologise, you are entitled to an opinion. Following your suggestion I have taken another look at the photo, and still consider that (in my personal opinion) it looks like a Common Sandpiper.
Personally I don't agree. I fully agree with your point made here and elsewhere that Green Sandpiper can show a paler centre to the breast (although I would usually consider that it is not as clear-cut as on the subject bird). However, on Green Sandpiper the darker sides to the breast cut directly across to the flanks, rather than creating a 'bulge' on the sides of the breast as on the subject bird (reminiscent of eg a Sand Plover or Kentish Plover).
Please check carefully who you are responding to. You will see that the location given in my brief profile lists my location as Hong Kong, not the UK (I was originally from the UK but have lived here for 15 years). Both species are common migrants and winter visitors here, I easily see 10-15 per day when in the wetlands. I am referring solely to my personal experience, and personally I see very few Green Sandpipers perched (actually I don't remember seeing one perched, but I may be wrong) but see this regularly with Common Sandpipers.
The legs are easily visible because they are silhouetted against a pale background. The tail (if it is present) would be against a dark background. The two are therefore not comparable.
Overall I personally still think that the bird looks most like a Common Sandpiper, and others clearly agree with me. You are perfectly entitled to disagree, and the image is fairly poor for judging with absolute certainty either way. Personally if I were the observer, based on these comments, I would leave this as an unconfirmed 'sandpiper sp.', but that is their personal decision to make.
! I'd prefer you just to help me id. the bird and not to start arguing about personal topics or points of views.
