• Several precious metal listings on Costco's website have had transaction limits tightened this year.
• Even with earlier restrictions, the company said its inventory sold out "within a few hours."
• Gold prices have reached record highs, and Costco has been a popular source for new collectors.

Sometimes things are a little too popular.

That certainly appears to be the case for Costco's gold bars. The wholesale club has been gradually tightening (and clarifying) the transaction limits on some of its precious metals products.

Where shoppers on Costco.com could originally purchase two one-ounce gold bars per transaction, they can now buy just one at a time.

And last year, Business Insider visited a warehouse in Wisconsin where shoppers could bring home a stack of five one-ounce bars.

Jumbo 100-gram bars are also now limited to one online, down from five a year ago.

The language on the product listing pages also better clarifies that "per day" in fact means within a 24-hour period — a distinction that previously had some social media users complaining about canceled orders.

Costco often uses item quantity limits for products where it anticipates strong demand for a sharp deal. An analysis of Costco's pricing strategy found the company sells gold for a scant 0.8% to 2.4% markup on average over the metal's spot price.

And even with earlier restrictions in place, the company said its inventory sold out "within a few hours."

The company did not immediately respond to Business a request for comment from Business Insider about the reason behind the tightened restrictions.

Beyond the price of the precious metal, which topped $3,400 per ounce last week, gold's popularity has surged at Costco, where novice collectors are drawn to the club's ironclad reputation for trustworthiness. One even characterized the club as a "gateway drug" to gold investing.

Some commenters welcomed the increased restrictions in discussion threads on the CostcoPM (precious metals) forum on Reddit.

"Good, they should limit to 1. Screw the flippers and bots," one Reddit user said. "It was getting near impossible to buy lately with the bots buying up all the inventory within a few minutes."

Other users pointed out that gold sales aren't about making a profit for Costco, they're about attracting and rewarding members, so it makes sense to allow more members to have a real chance at buying bullion. 

• The gold market is surging, briefly topping $3,500 an ounce on Tuesday.
• Costco sells millions of dollars worth of bars and coins for some of the lowest markups around.
• One buyer who's spent $30,000 on gold this year called Costco's offerings a "gateway drug."

With the gold market surging — briefly topping $3,500 an ounce on Tuesday — Costco is again a hot spot for precious metal collectors hoping to make a near-instant windfall.

The market for gold often rises in times of uncertainty, and the current price moves are driven by interest in the commodity itself as a safe-haven investment and by the depreciation of the US dollar.

One collector who has bought more than $30,000 worth of gold this year told Business Insider there's growing concern in the precious metals community about gold prices rising so quickly.

"To me, it is the measuring stick for how bad things are going to get," he said.

The person requested anonymity because of concerns about personal safety, but he provided BI with receipts from recent Costco purchases and documentation of his additional gold holdings.

He said he owned no gold until this year and only began collecting as the political and economic environment became more unpredictable.

Costco, which sells gold bars and coins online and in some of its stores, made it easy for him to get started.

"Costco was the gateway drug to gold investing," he said.

It's no secret that Costco sells hundreds of millions of dollars worth of bars and coins for some of the lowest markups around, but there are times when the market moves a little faster than the company's price adjustments.

In particular, several product listings on Tuesday — namely a 100-gram bar and a 1-ounce bar — were listed at prices so close to the spot market price that Costco Executive Members using the Costco Citi credit card could see a net reward of about 1% to 2% of the purchase price.

In other words, Costco is basically giving some members money to convert their dollars into gold (up to certain limits on individual and annual transactions, of course). Executive rewards are capped at $1,250 a year, but the company's credit card rewards on purchases are not limited.

Costco did not respond to a request for comment from Business Insider, but precious metals sales have been a key area of growth for the club's e-commerce business.

The company benefits from routing hundreds of millions of dollars in sales through Costco.com by simply buying a batch of gold and selling every ounce of it to members.

Other non-Costco credit card promos can make the math even more remarkable, as one gold flipper who bought more than $100,000 worth of gold last year attested to.

It's also important to note that Costco does not allow returns or price adjustments on gold purchases, and some buyers have found it unexpectedly difficult to quickly sell their bars and coins at a price that makes the flip worthwhile. Most collectors recommend building a relationship with a trusted local gold dealer to conduct transactions.

In general, the collectors BI spoke to are gold holders, not sellers, and the demand at Costco remains fairly steady.

"The price hasn't had much of an effect. The people who want it buy it," said one warehouse manager who requested anonymity because he's not authorized to speak to the media about sales.

The Costco manager said his location occasionally receives about 10 to 20 bars, which are usually sold within a week, and sometimes within a few days.

Costco executives have previously said that online sales can run through a batch of inventory "within a few hours."

As the price of gold dipped from Tuesday levels, Costco gold enthusiasts took to the Costco precious metals Reddit community on Wednesday to discuss the lag time between when the listed prices would be updated to reflect the market change.

"Costco doesn't real-time price like online bullion brokers," one Reddit user wrote. "Their pricing lags up to a day or two behind spot… which was great for customers buying when gold skyrocketed, sometimes Costco pricing was below spot BEFORE cash back… this is the other side of that coin."