It's really hard to tell just by looking. Mkeller is correct that the Melton sweated the details more so than whoever built the Raliegh Pro. But that does not automatically mean that the Melton design will ride better (assuming that both were built with the same kind of use in mind) or that the brazing on the Melton was done better or that it is more structurally sound. I'm not saying that such is not the case - and I would guess that the fit, finish, ride charateristics of the Melton are superior to the Raleigh because more time and care went into it - but I am saying that once you reach a certain level of food chain, it is hard, if not impossible, to tell which frame's joints are stronger or which one feels better to ride just by looking at the painted finished product. If you about brazing and metalurgy, you could tell more seeing unpainted frames because the effects of the heat from the torch are more apparent. But paint can do more than protect against rust, it can hide a multitude of sins.

Even a tubing sticker does not tell you as much as you might think. I have no idea what the tubing is on my Ron Cooper and, beyond curiosity, I really don't care - if he picked it out, it's good for the intended use, and Ron Cooper could build a better riding frame out of gaspipe than many companies could make with latest and greatest from Reynolds or Columbus.

That does no mean that a visual inspection is worthless, just that a visual inspection cannot tell you eveything you are asking about. The stuff mkeller points out - careful filing of lugs without leaving a bunch of file marks, lug edges that are crisp and don't have little globs of brass - indicate a level of attention to detail that, more often than not, means that the builder brings similar skill and attention to his/her torch work and to laying out the design. And it is the design and the torch work that really make the difference.

And you have to have both. Someone can be absolutely spot-on perfect in terms of getting the brass or silver to flow perfectly and uniformly into the joints and heating the tubes only as hot as is absolutely necessary and only for as long as necessary, but if they have no sense for how to design frames to provide the right combination of comfort, stiffness, stability and responsiveness for the intended use, the torch work is wasted effort. Similarly, you could be the most skilfull designer ever seen, able to match a rider to the ride tube set and right tube lengths and angles like nobody's business, but if you can't braze a strong joint or control the temperature of the tube, all of your brilliance will go for naught. (I don't know if Grant Peterson knows how to braze or not, but he sure knows how to design frames that work very well for many people and pays some first-rate torch bearers to execute his Rivendell vision. It's a smart division of labor, although it does add to the cost somewhat.)

Some of what you pay for with frames with a "name" - Albert Eisentraut, Richard Sachs, De Rosa, Roland Della Santa, and the like - is a premium for the certainty that you are getting a great riding, beautiful, well-made frame. You know it's damn good because there are literally decades' worth of damn good bikes out there that say so. (It is this factor that leads me to surmise that the Melton mkeller pictured is built better than the Raleigh - Raleigh's are generally good, but Meltonss are absolutely first-rate from what I have heard from owners.) There are plenty of lesser known or newer builders who can do just as good a job, but they don't yet have the track record.

A lot of the type of comments you mention - "X is well made but Y is not" - are the result of the word getting around about Y's cracking or not handling well, not from someone looking at the two of them and comparing the visuals. For example, no one knew that the infamous Lambert "death fork" was a structural disaster from looking at the bike just sitting there. If you took the fork out and looked at how it was made - and knew something about metalurgy - maybe you could have known. But nobody did that until the forks started to fall apart. In terms of structural integrity, the same is going to be true of most frames that actually make it to market in any numbers. Handling issues are somewhat different - there are certain elements of fork rake, frame angles, seat stay length, etc., that make reasonably accurate guesses about how a bike will handle pretty easy.

So while your question is a good one and well worth revisiting every so often, learning about the visual clues will never be the be-all-and-end-all of figuring which frames are top-drawer and which ones aren't.