Quoted from Lighthawk (Re: the traps in the simulations):
I actually think the traps are quite appropriate for a thieves guild of the size we are attacking, but the guild is far too big for a town of Howthen’s size and would be more appropriate for a small or medium city. But as you said yourself it is just a simulation and we wanted a tough fight. I think I can easily promise a very tough fight
Rouges in D&D are supposed to be expert in finding and disabling traps, so it seems reasonable that they also have a good idea about making them, the crossbow trap is actually fairly simple to make and this particularly guild has a mage of their own so a magical trap should be expected too.
Rogues are experts in setting up traps, this is true; however, the problem that I see with these traps for an ordinary thieves' guild, in any city of any size, is this: these traps require preparation and sophistocation.
It is absolutely reasonable for rogues to create traps that fire crossbows from a remote trigger, but the trigger must be something they can wire to the trap. A tripwire, or similar triggering mechanism, is fairly easy to rig, and so it would be quite understandable for rogues to have rigged such a trap with such a mechanism. These crossbows, located in slits in the cieling, however, require that a special room be built in the cieling for them. The trigger mechanism must then be strung through a cable, which has to run behind the walls (or else we would see it), and under the floor, all of which also need secret chambers behind the walls and under the floors, to attach to the raised tiles. This sort of job would require a week of building to make, so it's not something that could be rigged on a minute-by-minute basis. The dragon-heads, likewise, must be glued to the wall, and making them (they being magical devices) would take time.
Now, this isn't very consistent with a thieves' guild of any size, at least not in a city with functioning civil order. What would the thieves do, for example, should the city police find their hideout? Under normal circumstances, they would have to abandon it, and not come back, because the police could lay some ambushes of their own. Since they are faced with the prospect of establishing a new retreat in a hurry, it seems illogical for the thieves' guild to put the time and effort required to make traps of this degree of sophistocation, the skill to make them notwithstanding.The most reasonable place to find this sort of thing in a thieves' guild is if it is the thieves' guild, not the municipal government, that is the real law in the town, and that the thieves are strong enough that they could actually defeat the municipal police in a fair fight, or else have bought them out (i.e. the police themselves belong to the guild). In that case, however, this organization is hardly a thieves' guild - it is a corrupt, behind-the-scenes municipal government.