Just got back from an another LGS that just received a 2.5" 686. They had it marked at $728.99 for cash. Had a perfectly straight barrel and locked up very tight. Thought I had finally found one that was put together right. Then I saw the scratch on the side of the top strap - not too bad, in fact I was willing to live with it.
However, I then noticed what looked like a circular rust spot on the side plate, near the recoil shield. Sales lady gave me some CLP and we tried to rub it off, but no luck. It appears to be some kind of chemical stain that discolored the stainless steel on the side plate - just ruined the cosmetics of the gun.
So, the search continues.
Regarding the canted barrel issue. What the other posters stated is correct. The 686 models have ribbing on both the barrel and the top strap of the frame. Those rib lines should line up perfectly as you move from the barrel onto the top strap. As others stated, if the barrel was screwed into the frame too far, or, not far enough, the ribbing on the barrel & frame will not line up. Depending on the severity of the "cant" it may or may not have an impact on sighting accuracy. But it sure ruins the cosmetics of the gun and gives the impression of a sloppy assembly. The 2.5" model I looked at today was dead-on perfect.