Just to belabor the subject ad nauseum:
That phrase made me lol
There are some growers that can identify a flytrap from photos, but generally only the more unique ones. And even then, who's to say it isn't a seed-grown that happens to look similar?
If a flytrap is in front of an experienced grower, it won't really help much compared to detailed photos. B52, DC XL, and Big Mouth are just not unique enough to positively ID in an unlabeled pot. Even unique flytraps like Pom Pom and Biohazard can't be identified 100%, as any flytrap can mimic these mutations, but later show other traits that give them away as not the cultivar they pretended to be.
We could theoretically look at the trap size of a possible DC XL and assume it is what it is, based on all information (source, etc.), but it would still be an assumption. The most obvious answer of course would be to measure the mature traps, and even then, not all DC XL's/B52's traps are "max size", so you could easily be looking at a colorful seed-grown that looks like B52/Big Mouth or a large-trapped upright seed-grown that just tossed up a 1.9" trap, and since it looks like a DC XL, you then assume it's a DC XL. This is bad practice, though, and should never be done unless enough information is available to make a 100% certainty deduction.
An example: If you know that your flytrap is either "this" or "that", or even "one of these 6 cultivars", an experienced grower can sometimes deduce from there.
Another issue is growing conditions. A B52 in epic lighting will look far different than a B52 that only gets 3 hours of light per day. Color, size, growth, will all be different. Also, flytraps grown indoors can often look far different, especially coloration-wise, than flytraps grown in sunlight. How much they eat is also a factor (the less they eat, the more colorful they are).
Again, the key phrase here is reputable sources. I'm sure there are lots of mislabeled flytraps floating around out there.
Here are three flytraps. Which is B52 and which is Big Mouth?