A villainous Salesdemon with a terrible checkered suit. He will sell you the equipment that you need for your quest, but he does not take to shoplifters.
Braxes are shopkeepers in checkered shirts. They own and operate shops on every floor of the dungeon, where the hero may buy and sell equipment and consumables. It is possible to steal from Brax's shop, but doing so will cause him to attack you and summon a Dread Collector army, which will probably result in a swift, messy, unpleasant demise unless you prepare adequately.
If you click on the items displayed you will get a dialog asking if you wish to "Buy", "Do not Buy", or "Pick Up." Picking items up allows you to place them on the floor or into your inventory. If an item is picked up without being purchased, be it to the floor or your inventory, Brax will change position to block the exit to his store. When an item is removed from its display case you may drop items onto the empty display case to sell them. The item will then take up that space and be kept in the store permanently, whereas if you sell an item by any other means, the item is lost when sold. If you try to sell an item you have picked up, not bought, from the store to Brax, he will tell you to stop waving it in his face.
Although rare, if a Gargoyle based trap is put into the store as a trap (it will not work however), upon picking it up again Brax will consider it theft and block the exit. You can just put the item back to leave the store safely. If you transform it into lutefisk or destroy by any other means, you will be stuck and have to face Brax in order to leave the store unless you have the Digging Ray Golemancy skill, or a teleportation skill.
Ironically, a cleared-out monster zoo can be one of the safest places if you have incurred Brax's wrath, as Dread Collectors will not spawn there, allowing you to kill them as they come and try to avoid being cornered.
Stealing from one Brax will thusly anger every Brax on that floor of the dungeon. To stop any additional Dread Collectors from spawning, then, every Brax on that floor must be killed. Doing so will prevent more from spawning, but will not remove any that have already spawned in, and there will probably be a lot of them. However, Braxes on other floors of the dungeon will not be hostile unless they are also stolen from.
While in Brax's shop, you can open up your inventory and hold down shift and left click inventory items to quickly sell them to Brax. Additionally, you can place items on empty pedestals to sell them.
It is possible to steal from Brax. However, it is also very difficult. Firstly, ensure that you have done EVERYTHING on the floor you plan to steal from, as you will not want to be coming back, ever. This does not apply if you are strong enough to kill every Brax on that floor, and then the seething horde of Dread Collectors who will still be eager to pummel you into protagonist pie. Doing so will stop any more Dread Collectors from spawning.
There are several primary methods one may use to steal from Brax. The first, most obvious one is by brute force. If you plan to do this, you'd better bring along some very heavy-duty armor, and a decent shield, along with skills to boost both, because both Brax and his collectors pack a serious punch. They are quite weak in terms of health, however, so grab the most hurty weapon you can find and go to town until you run out of angry red things to hit, chugging potions and eating food as required. Several spells, such as Psionic's Force Shove, can help immensely, as they will allow you to push back the Dread Collectors to give yourself some breathing space.
The second method is by guile. The Burglary skill tree allows you to steal one item without fear of being caught, but as you cannot choose the item, this method is significantly less attractive than the other methods.
The final, and by far most practical, method is via magic. Teleporting out of the shop while carrying stolen merchandise will not alert Brax - so long as you do not move other than by teleporting. Moving without the aid of teleportation will instantly alert Brax to the fact that he's a few million Zorkmids poorer, and he will immediately come after you to take his grievances up with you directly. As such, teleport your way to an exit, run down a level, and never, ever return.
You may also use Force Shove to push item pedestals out of the shop completely. However, taking it will still alert Brax once it's out of the shop as soon as you move, so if you can't get it to an exit, don't even bother trying this. Additionally, upon trying to leave another store, the Brax who owns that store will see it as you stealing from their store, and promptly set the Dread Collectors on you.
It should also be noted that using any kind of transmutative spell on an item from a shop will cause Brax to block the shop's exit. As you will almost certainly have irrevocably destroyed it by using said spell, this will trap you with no way out other than killing Brax, so it's not a good idea to try this.