I am openning a shop. What equipment should I sell

First thought in my mind is, why are you asking us? We don't know your market. What is your competition selling?
Sell something different to avoid price wars.
What price range will your client base be willing to pay?
Don't sell to high-end or they will pass you by.
What products are represented in your are by good distributers? See if they will do some consignment to get a feel for what people will bite into. What are you trying to attract most? Analog, HT, Stereo, mid range, high-end?
I wanted to do this a few years back and realized that the market was too competitive and the industry is too unstable. But best wishes

I would only do this as a hobby, I don't think you can make a living with 2 channel. Curiously I get the sense that the market is becoming larger but at low price points. If you are going to take the plunge follow Theos advice and find a niche and also be prepared to be a specialist in HT. Whatever you do don't undercapitalize and be prepared to work really hard selling yourself.

Anything but Audio equipment.

A lot of the long established "2 channel" outfits, are now more into high end home theater and custom installation. That seems to be where the money is retail.

They all still sell 2 channel, but it takes up less floor space than before and/or if there is lots of space, the 2 channel is in the back of the store.

What is your target market?

Are you going to do both 2 channel and HT?

What brands are not sold in your area?

What brands have multiple retailers in your area?

Are you going to do installs and POS or just POS?

Is it going to be a Hi-Fi shop only?

Bass (not base) response is important to some and not to others. Depends on if someone is going to use a separate sub or not and what type of music they listen too. Also how big the room is. Among other things.

I think you should sell at price points that sound good. I would never sell something that sounds bad to make a buck. If you did, you will not be in business for too long. Sell people a good quality product with good service and you will get repeat customers.

No offense, but if you don't know the answers to your questions already you probably need to hire someone to run the shop for you that knows the answers.

Good luck.