With magnet?

I'd send some current through it to warm it up with 1/4W if that's the rating and see what the resistance is when it's hot.

Then compare drift to a typical metal or carbon resistor. Carbon should drift way more than metal film I think.

 

Once you find a supplier who sells quality stuff, stick with that supplier for future purchases.

That doesn't always work. I bought some 1.5Ah 18500 LI-ion batteries from a seller on AliExpress. That was before I knew that many/most of the listings are fake. After getting some fake 18650's, I went back and tested the 18500's. I was fortunate that all of them delivered around 1.4Ah.

After getting so many fake 18650 and 16340 batteries, I decided to use 18500's in my flashlights that took 3 AAA batteries. So I bought 20 1.6Ah 18500 batteries from the seller I bought the first batch from. Batteries were from the same manufacturer, so I thought I was home free. Wrong. The batteries provided 800mAh-1.1Ah. AliExpress fought me on that dispute, but they eventually gave me a full refund.

I don't know if the batteries were rejects or the manufacturer became disreputable. In either case, I'm still not inclined to use them.

 

I bought a huge set of resistors from ebay like 18 years ago or. This was all packed away but recently unpacked as I've got my new workshop setup. The values are basically every value that's made and the tolerances of 10 and 5, the entire batch fills a cardboard box that was a case of wine.

I've never found anything out of tolerance, naturally I'm never going to use even a tiny fraction of these but they seem absolutely fine.

 

A 68K resistor out of that box measures (after settling) at 67.540 in "slow" mode, using this DVM:

 

I'll be doing another pass. I have an QuicKutz scrapbooking tool that I use now.

Second pass with the QuicKutz. I only used needle nose pliers on the ones with kinks too close to the body for the QuicKutz to deal with. Took a couple hours.

Next, I'll sort them by package type and then by part number.

 

Took me about an hour to sort them. About 400-500 diodes and a couple dozen different values.

 

But they don't "match" one says 9.66 the other 9.688. The latter (when rounded) would be 9.69 - that's not really a match.

A few years back I ordered a carbon resistor kit off of ebay. They were sold as 5% they all had the gold band. I made a circuit using some of them. It didn't come close to what I was expecting. I took it apart and measured the resistors. The first on was off by 15%.
I randomly checked others in the kit and found that most of them way oit of tolerance the worst being 22%. I didn't waste anymore time. I tossed them all and purchased a kit from Newark. Much better results. Since I have stayed away from EBay.

 

A few years back I ordered a carbon resistor kit off of ebay.

What type of carbon? Carbon composition or carbon film? Carbon comp resistors are expected to drift with age. If they're carbon film, it sounds like you got components that were pulled from trash.

Regardless, counterfeit/fakes are such a problem on eBay that I won't buy any components, especially if they ship from China.

Before counterfeiting became such a big problem (up until around 2012), I bought hundreds of thousands of resistors, caps, etc. But I rarely bought from anyone who had a store. Buying from sellers who seem to be selling odd lots of things felt safer.

One of the times that I bought from someone with a store who appeared to be buying in bulk and repackaging left me with a bad feeling. He was repackaging CMOS IC's on florist's foam and putting that in plastic bags. When I complained, he said no one has ever had problems with that. He had good prices on axial ceramic caps, LEDs, and crystals. The price on the IC's was good, but not when I had to consider reliability from exposure to static electricity. And now I worry about his handling of the crystal oscillators because they can be damaged by mishandling (e.g. dropping them).

 

A “10K”, 1 percent, metal film (I hope) resistor from ebay:

9,688 ohms

That would be a 3.22 percent resistor.
Sigh.
View attachment 311410

I purchased a mix of 5% carbon resistors. I used three in a circuit and the circuit simply didn’t work as I was expecting. I pulled out the resistor and measured it. It was 23% .
I started measuring more from the kit and found that most were well beyond 5%.
I tossed them all. Since I buy all of my components from trusted sources.