Costco (COST 1.01%) sells a shocking array of products that people may not associate with the brand. Yes, the warehouse club specializes in bulk groceries, household items, and other grocery store/pharmacy staples, but it also goes well beyond being a place where you can get a deal on a six-month supply of deodorant. Costco will help you refinance your mortgage or help you set up business payroll services.

Of course, not every product or service the chain offers is clearly a great deal. But there are tremendous savings available, perhaps on things you had no idea Costco sold. As is the case with any deal, make sure you shop around and don't just accept that any one chain always offers the best prices. That said, here are four things that you may not have considered buying at Costco, but in many cases you should.

Costco does not show all of the things it sell on store shelves. Image source: author.

Engagement rings

"Costco is one of the best places to get a smart deal on diamond engagement rings," CreditMonkey's Charles Tran told The Motley Fool in an email interview. "The $55 membership fee can save you thousands on a ring."

Tran explained that it's simply a question of volume. Costco has purchasing power a small dealer can't match. What potential brides- and grooms-to-be give up in exchange for paying a better price is selection, with the warehouse club carrying a narrow selection of designs. The chain also has customers covered if the person receiving the ring either turns down the marriage proposal or disagrees with the choice of ring.

"While Costco does not allow you to customize your ring, they do offer a generous return policy," said Tran.

Hearing aids

Costco sells top-quality, name-brand hearing aids under its own Kirkland brand name. It also has in-house, salaried technicians selling them and fitting people for them. In much of the hearing aid industry, salespeople/technicians work on commission. That could lead the person making the sale to steer the customer to products they don't need or more expensive models. That won't happen at Costco where prices are generally lower than at dedicated hearing aid stores and the salespeople are not incentivized by how many units they sell.

Business accounting software

It seems silly, but the warehouse club offers QuickBooks Online, the standard for business accounting at a discount over subscribing to it directly. That makes sense because Costco has millions of business customers and Intuit (NASDAQ: INTU), the maker of the accounting software, likely sees offering the chain's members a deal price as a smart marketing tool.

Intuit offers Costco members a free month, plus a 30%-40% price break for six months depending upon how long they sign up for. These are not the only deals the software company offers, but they are among the best (if not the best) discounts regularly offered on QuickBooks subscriptions.

A new car

You can't buy a car at Costco, but you can buy one through the warehouse club. CreditMonkey's Tran told The Motley Fool that this is a surprisingly risk-free way to purchase a new vehicle.
"Costco offers members a great way to buy cars. Like the case of soda at Costco, you might find it a bit cheaper somewhere else. But what Costco offers is a good fair price without the hassle," he wrote. "You won't pay through the nose when you buy a car through Costco's auto program."
Basically, buying through the chain's program takes the guesswork for customers. They may not get the absolute lowest price, but they will know they are getting a fair deal.
"The hardest part of negotiating car prices is the sense that you don't want to get ripped off. Nobody wants to get the raw end of the deal," Tran wrote. "At Costco, you don't get ripped off. Costco is looking to build customers for life, not to make an extra $500 on a one-time sale."