latest?
greatest?
inventory?

customers.

Nah.
People buying stuff and (especially) services. And telling other folks about it.
Owner and staff being cheerful, helpful and non-judgmental.

A shop that's owned and paid for already.

Good customer service and great mechanics.

After having a shop I worked at with great customer service, great mechanics, and that owned it's own building close down, I'm inclined to believe the answer is luck.

It needs to cultivate the right customer base. Yesterday I was in my local big-brand retail/service outlet. One couple came in and within 15 minutes dropped almost $10k on his-n-hers carbon 'endurance' bikes.

Meanwhile, at the service desk, another customer was engaging the head mechanic on a tedious debate over the right kind of waxing regime to extend the life of their $10 chain. At a charge out rate of likely $200 per hour, and no shortage of work to be done in the back, this customer effectively cost the shop $50.

Meanwhile, I was filling a box with discounted consumables such as cassettes and chains that probably cost the shop wholesale double what I paid for them. I will then take these to fix my bikes and those of my (rich) pals thereby taking away business from the shop.

So which type of customer should you cultivate? Hint: you want customers who roll up in a Porsche SUV, pull out a $10k bike for the scheduled semi-annual servicing ($300), and trade-up every other year. All done with a Platinum card.

I spent about a dozen years in bicycle retail, beginning in the middle of the Bike Boom. I would have to agree that a lot of a shop's success is due to luck. I think the biggest factor is location, as I've seen quite mediocre shops be successful or even thrive, largely because they have a steady stream of new customers. Professionalism, tempered with approachability and a commitment to customer service and satisfaction, community engagement and effective marketing are all assets, as is specialization, which is especially important for smaller shops.

I have a Rodriguez tandem and it's the most comfortable and most versatile of our several long bikes, but I have to say that their secret sauce can't be applied to other shops. First off, the country doesn't need and won't support even one R&E type shop in each city. What a shop should have is relationships with specialists who perform competent frame repairs for each common material. People don't come into shops for product, they come in for solutions. They want to recognize experience and a broad knowledge of the industry, technology and trends, and they want the assurance that any problems they experience will find solutions at the shop. For most customers, it will be a big plus if the staff come across as supportive, non-elitist, and non-judgmental and, most importantly, if the experience is as much fun as they expect their cycling to be.

Location. Upper tier incomes surrounding.
Those attributes are tough to find at a rent factor that is durable.
I have seen a few shops needing to move way too frequently.

one shop I worked for was really smart, they had a 50 year lease, sold off the shop for basically the lease and fixtures.
that shop ran it until the lease was up.
then left, 25 years for the follow on shop.

fifty year leases are gone now.

One LBS around here that’s lasted a long time is the shop in the local REI. I imagine it’s easier to work out the financials that way (and they do solid work).

Finding customers that pay for your time.

A very good customer focused and oriented business. I would ad also ability to repair frames, build custom wheels as well as repair all kind of shifting. The lbs I always go since the last 15 years is existing since 25 years has always had an approachable and extremely well customer focused owner who worked at mavic and at decathlon as well as who worked at cyfac.His costs are reasonable and the quality of work always top notch.

Niche helps. It isn't compelling to supposedly be good at everything, but being renowned for a few things guarantees a certain core customer base

To ask the original question slightly differently, what are the most profitable (bread and butter) goods/services shops count on to keep money coming in?

You can make a small fortune with a bike shop, but first you have to start with a large fortune.

The nearest shop to me (Waterfront Bicycle Shop) is very small. They don't sell new bikes! There isn't room to stock them. Somehow they get by. They do repairs, they rent bikes. It's a touristy neighborhood. They sell parts and accessories, and they usually have a few used bikes. I've seen the owner build some project bikes and put them up for sale, such as something with a Velo Orange frame, but that may not make any money.

And be good to them. There is a shop close to my house and the owner is a great guy, but his service manager is a flaming (insert banned word here). I really wanted to give them my business, but the service manager jerked me around one too many times.

Same with airplanes

These guys are insecure, think they should be in charge, dictate how you and I work on our bikes, too bad they can't get out of their own way, they can be the death of a shop on their own.

Assume you had a candid talk with the owner on the matter?

They were at MADE, great gang, great stuff and great work.

Like they said, there is almost nothing they won't take on and literally make it better than it can be.

Another thing: low ratio of cheap b@st@rd C&Vers in the immediate area.

Mergers.

I'm sure that's true, so I'm very surprised when my LBS owner seems glad to see me. He likes to chat for so long that I feel bad for taking his time. He also likes me to take his bikes around the block to test them.

I try to patronize LBSs and order online only when I have to. But gee, two LBSs have told me they don't want to special order for me and that I'm better off buying on Amazon.

Bikes are the least profitable at only a 33% margin, give or take. Service, parts, accessories are much better. The problem is getting people in the door when they don't have new bikes to offer.

That's exactly right. This one guy has figured out how to make it work for him, but it may not be possible for other shops. He's in an unusual area. His repair business is pretty steady. I think he is selling merchandise (accessories and components) at a decent rate.

Two blocks away from that shop, we had another rentals-and-repairs-only bike shop. It survived for a few years. The owner claims Citi Bike coming in ruined him, and I'm sure it was a factor, but I don't think that was all of it.