Variety, enough space to set up and look through boxes/binders easily, books and accessories, fresh inventory, good lighting, reasonable pricing, accurate grades, knowledgeable and friendly staff, convenient hours.
Here is a coin shop I go to in my area: 1. Well organized and clean with nice display cases. 2. Friendly, knowledgeable owner concerned about my collecting interests. 3. Willing to negotiate sensibly (meaning I have to have sensible expectations). His prices are fair to begin with. 4. Willing to keep an eye out for a particular coin for me and follow up with contact if he gets it. 5. Enjoys just talking about the hobby, from which I can learn a lot. 6. If the store burned down, I would cry and offer to help the owner. Here is a coin shop in the area that I had the misfortune of going into once, and hopefully the only time. 1. Owner is in desperate need of a personality transplant and remedial manners. 2. Ten years worth of price guides strewn out on the floor. Dust guarantees that if you don't buy a coin, you will still get a free hay fever attack. 3. Virtually everything kept in a safe, virtually nothing on display. 4. I can "check back" to see if he comes across a coin I'm interested in. 5. Can't properly service a new customer because he's holding court with a bunch of old cronies who voice their opinions (unsolicited) about the customer's interests. 6. If the store burned down, I would hope that no firefighters were injured.
Good selection of coins in all grades, whitman bookshelf albums, and a big container of inexpensive foreign coins to go through.
Aside from similar thoughts that others have posted, in today's day and age, I like to see an online inventory. At least the major selections, not necessarily every common cent, but anything certified or valued above $25 should be at least on a list. Maybe it's my background in internet marketing speaking, but... a web presence is going to continue to be vital, likely more so as the years pass.
Reasonable prices/margins. One of the local coin dealers in my area is very friendly and personable, has excellent customer service, occasionally has nice coins BUT they price everything extremely high and after haggling their prices are not competitive. So I don't purchase many numismatic coins there and another local dealer gets my business despite being much further from my home. The combination of decent pricing and nice coins gets me in the door.
Friendly, knowledgeable people who will stir a conversation, decent selection, reasonable prices. Also, some good personalities with a little interesting talk. I am fortunate that I frequently attend a shop that provides this regularly, but there are other shops where you shake your head and wonder how they stay in business.
My local dealer is a past president of the ANA, and former editor of the Red Book. Guess what? As he ages, his adult son (in his 40s I believe) is taking over most of the business operation, and it just so happens that the son is also an ANA past president and Red Book editor. Needless to say, there is a LOT of experience between them. One thing they have going for them is reputation. They are honest. Although the store takes several employees to run, all of them have a certain degree of numismatic experience and the owners demand the same level of integrity out of their employees that they themselves exhibit. There are other coin stores in town I will never set foot in again, ranking slightly below the average pawn shop in my opinion.
Friendly customer service is a must. A good selection of all price ranges. I had a place in Florida I went to, and the owner knew what I was interested in. When I came back each time he would remember me and show me what he picked up since I was last in which really helped grow my collection..
Reasonable prices. I recognize stores need to make money, so I don't expect rock bottom prices nor do I ask the store to go lower. Being a repeat buyer from my local stores, the owners give me discounts at times, which is really cool. I also like variety. That includes classic AND modern. Not all of us can afford the old stuff, so to be able to get something modern at a cheaper price is great. And finally is the owners are accessible and not rude. Nothing turns me off more when an owner ignores me. I am a bit younger than your typical coin collector and dress in an unique fashion, so I tend to be avoided by people. Happens a lot at shows and thus I take my money to another table. Their loss not mine.