@jmarsh Yes, have to be careful.
Look for a third-party seal (like USP, NSF, or ConsumerLab) on the label to verify the contents.

I subscribe to Consumer lab . They test products for purity. And discuss legitimate studies that have shown efficacy for the condition you are taking it for..
I've always taken Carlson Labs fish oil. what I'm taking now is MaximumOmega 2000. Carlson lab is not cheap though. It is the triglyceride form .
Nature Made which you find at WM has passed in their currant round of fish oil. Kirkland from Costco has also passed. Neither of those is as concentrated as what I'm taking now.