The work being done by ConsumerLab is really useful, but of course one has to pay for it. They are not quite so concerned with the source of the ingredients but they do laboratory testing to find out how much of the nutrient or principal is actually in the product and what the variation is. A label-focused approach, unfortunately, leaves a wide space for nearly outright lying in this field. For example, you can find 1200mg fish oil capsules that do not weigh 1200mg, including capsule. They may be filled with fish oil or with a mix of fish and other oils. The fish oil could be depleted of certain fatty acids after making an enriched product that is sold separately. Other supplements may claim to be herbal medications but are actually adulterated with the prescription medication to achieve an effect.
Current Good Manufacturing Practice is a good thing but in the supplement industry is mostly an attestation. Unlike drugs, supplement manufacturers are usually not evaluated by the FDA unless they have collected evidence of problems at the facility. It requires people designated as quality control officers, written practices, and storage of samples, but, unlike drugs, nobody checks this stuff before a supplement is sold. The supplement industry has had some powerful congressional allies, and it is possible that too much regulation would cause congress to revoke the FDA's authority over supplements entirely. (My speculation).
Another standard is USP. This standard includes GMP and goes beyond it, with verification of potency, vehicle breakdown/release of ingredient, and measurement of contaminants.
There are several well-known brands that are consistently on-target with their supplements, and others that are frequently off target. I haven't reviewed the data recently so I won't list them here.
https://www.consumerlab.com/
https://www.usp.org/dietary-supplements-herbal-medicines
https://www.quality-supplements.org/