That funny little tie and not immediately violent demeanor isn't fooling anyone. This guy is not your friend and he is not there to help you on your arduous task. He wants all your hard-earned artifacts no matter how early and poor you are in the game.

In this guide, I hope to teach you how to show these silent enemies that you are onto them and there's nothing they can do about it. I will be covering the best methods I know and including the occasional optional action during some of them.

Method 1 is one of the least effective ways of getting all his stuff as it often involves putting yourself in great risk given the Shopkeep's toughness and, on hard mode, high damage output. The upside of this being that the amount of stuff he drops is considerably larger than that of the day to day plebs you punch in the face.
Method 1.5 is a bit more effective wherein you lure him far away from his shop, loop around, and then take everything you need while he is looking for you elsewhere. Keep your eyes on the door while looting because getting hit in the back sucks after you already ate his two entire Dungeon Hams™. If he returns to his shop before you find a way to, he will naturally be looking away from the entry and all his stuff, so as long as what you grab doesnt swap and drop, he wont notice.
The biggest upside to this is that if you have just started the game and have nothing to lose, you can make straight up profits by giving him that black eye he probably gave his spouse.

Method 2 involves minimal violence but requires the Cloak spell, artifacts to use it it (10 or 5), and preferrably the Stealth Boots. To make the most of this, it is important to know what you want from his shop beforehand so you can make the whole run on a single casting of the spell before leaving him to wallow in his crocodile tears. If you have the Stealth boots, go ahead and run around the shop after grabbing his stuff and maybe fart next to him if you had one coming on. You have the time. On the other hand if you don't have the boots, you will want to walk your route and leave because running will make him throw fireballs at random towards where he last heard you and that can be even more difficult to dodge due to the random spray pattern. He will always be hostile if you steal something, even if he never once saw you, so don't go back expecting him to tighten up his bowtie and brighten up his smile.

Method 3 is one of my favorites because of the cheap cost and general usefulness of the Materialize Spell. You can leave his shop with everything you could want from it for the cost of 5 artifacts (totally free with the Conjuror's Talisman!) So go ahead and dance and laugh at the crooked merchant in his new cage as you load another 6 shots into your favorite firearm. For added fun, use the materialize spell to make this store into your new home, maze, or fortress.

Method 4 Requires the Pick (found in the Halloween pumpkin land or Mountains of Madness) and at least 2 good hits out of it (which is basically never, amirite?) or the Destruction Talisman, a Revolver and at least 2 bullets. You need to be extremely careful doing this because there is only a tiny spot on each corner of the cube the Shopkeeper stands on that you can hit, and the last thing you need is to accidentally hit him in the lovemaker while you are on your knees between his legs. This is particularly hard outside of Worlds 1 or 2 given the shopkeepers larger size, but is arguably the funniest way of disabling him if you also have the materialize spell to cap off that hole you put him in. Insert dynamite or shoggoth if you are feeling particularly vindictive.

If you are up for some sport and have some Dynamite handy, I highly encourage this method. It is a well established Law of Dagon, that you ignore the smell of sulphur accompanied by a hissing noise while operating a store front, thus, those operating outside the Law of Dagon may happily place a block of dynamite right at the Shopkeepers feet.
Placement is everything!

It may help to crouch down a bit to get a more accurate placement because the objective is to send him up and back against the wall then plummet down the hole to the floor below. The upside to this is obviously that it is hilarious and relatively cheap if you've been finding a lot of explodium.

Method 6 is a bit riskier than others because you have to lure monsters into the shop and get them to hit him and start a fight. It is however, more effective on higher world levels due to the denizens being generally tougher. Shoggoths are the best option for this trick because they can't die and their attack animation is slow so it's easy to dodge while the shopkeeper gets a good taste of that thick slime tentacle right in the mouth. If you don't have access to that, any other monster will be fine for at least a hit or two unless you have the Hypnotize spell which will make them actively target the shopkeeper and fight him to the death, though both types of beetles will automatically act agressively towards him. Also, mind the crossfire.
Method 6.5 involves having an enemy hit dynamite in his shop, whether he is selling it or you put it there on purpose. This will cause the shopkeeper to act hostile towards the thing that detonated it and afterwards you are free to take any items you want without any struggle, even though it says "examine" when you hover over the items. This is likely a glitch involving his product being stolen or otherwise tampered with by an entity other than the player which would would normally disable the shop function in the game.

So there you have it. What's his is yours. I Hope this guide has given you some new insight on how to aquire gear in Elritch more easily or at the very least more entertaining. If you have any more ideas on how to take his stuff without dropping a single artifact on the counter, leave a comment.