There are of course interesting applications of powers like these in realms like combat, terrorism, ideological revolutionary activities, and villainy. (Frankly, the 2-second charge time would not dissuade any army from using their hammert troops to delete 1.28 cubic meters of steel or 4.5 cubic meters of stone each. Especially when they can each do it every 2 seconds) But I'll confine this answer to the subject of the question: preventing theft.
The answer will have to be something of a frame challenge: in a world such as you've described, hammert theft cannot possibly be an issue, except in the rare cases of sentimental objects being stolen in small, personal ways, as between friends or acquaintances. Or, perhaps, capers and schemes to steal major unique works of art. In either of these cases, standard preventive measures would be considered enough.
Why would hammert theft be no issue at all? Well, simply because none of them would have any desire to shoplift or steal anything. They'll simply be too rich to need to. Allow me to explain why.
All the work of the world boils down to only 2 things: (1) uncertainty, and (2) relative position.
(1) Uncertainty is simple enough. It's the basis of investment, marketing, research, all that stuff. It's just asking (and trying to answer) the questions like "will the harvest be good?" "Will this product sell?" "Will this company succeed?" We do a lot of work trying to figure these things out.
(2) Relative position is about getting things where you need them to be. You have a load of lumber here, and you need it to be in London. You have a lot of seeds, and you need them to be in the ground. You have a lot of stone at the quarry, and you need it in the walls of the castle 10 miles down the road. &c, &c, &c. We do a lot of work trying to rectify the discrepancies in where things are, and where we want them to be.
Hammerts have little effect on the first, but they absolutely upend the second, throwing most of it out the window. Hammerts transport infinite amounts, with perfect certainty, and a loading/unloading cost of 2 seconds per 10 metric tons. This is groundbreaking. Even if you rule that they can't teleport boards of wood out of trees, or chunks of rock out of the ground, they still revolutionize logistics. Suddenly, instead of needing to ship thousands and thousands of tons of lumber across the country, the continent, the globe, you just have to send one little orange man. Even if he dies on the way, the payload will just devolve on his heir, and can be recouped. No longer do castles need to be near quarries, no longer do cities need to be near rivers or the ocean, no longer does anyone have to be impeded from doing anything practically anywhere just because it would be hard to source or transport resources there. As long as a single man can transport a child by some means (wagon, canoe, balloon, horseback, dogsled, carrying... &c &c), there simply isn't any sourcing or transport issue.
The only things that would need to be actually transported, physically, would be those things that can't be broken into pieces of 10 metric ton mass. (Since the density limit for using all the volume of the hammert power is 0.5g/cm^3, the mass would always be the limiting factor. 0.5g/cm^3 is the density of gases, not solids). And since these would be the only items being transported physically, the demand for them would drop precipitously. We're looking at a world where the only discrete objects with mass more than 10 metric tons that exist are those that absolutely positively must must must be that massive. Everything else would simply be redesigned so that it could be transported by hammert.
So, then, why no theft? If all creatures had this ability, it would necessarily become relatively worthless. Like reading and writing, which take a dozen years or more to learn, and enable a frighteningly wondrous array of things, but which are so ubiquitous nowadays that their value in-and-of-themselves is nil.
But this is an ability held only by hammerts. Which is to say that there are a great many people who need this ability, but who cannot get it except from the hammerts. And this is a situation crying out for organization. Whether it's the hammerts who organize it, or the more physically able races that would rule (and protect) them, either way there's going to be a hammert guild. And, frankly, I believe it would be a "hammert guild", and not a "transporter's guild". Because there simply wouldn't be a hammert alive that wasn't a member. Their skills are by and large too valuable to be wasted elsewhere, and if there was a great scholar or religious figure or business magnate who somehow could justify (to themselves and others) not being a transporter, then they would certainly be under an agreement with the guild not to use their abilities personally in any but a private capacity.
As a result, transport would be quite cheap (compared to reality), whilst still being ridiculously remunerative for the hammert guild. And while there would certainly be a pecking order, it beggars belief that there could be a hammert anywhere who wasn't both respected and prosperous, not to mention civil to a fault. Hammerts would be seen in fine clothing, with bodyguards and attendants, moving constantly upon the roads between each and every settlement, perhaps even with a religious solemnity to their "great perambulation". And if they wanted anything that could be shoplifted, you know that they would be able to buy it. Even if not, the guild attendants couldn't let their charge be caught up in any kind of activity that would imperil the reputation of the guild or the timely delivery of their cargo. And these attendant retainers would be omnipresent, at least in public.
