There's this company that offers free testing: https://finnrick.com/
Another popular testing company is https://janoshik.com
Some other useful resources: https://graymarket.substack.com/ and https://glp1forum.com/
There are a few subreddits as well.
FWIW, I never ended up buying any myself.
Where do you think Hims, Ro, Brello, or the rest get the APIs they sell to their customers? They get them from grey market suppliers in China. They don't go to Ely Lilly or NovoNordisk and say, "politely sir, may I skirt around your IP and sell your drugs for 10x what they cost instead of 10,000x what they cost?" Hopefully, they test them and filter them and use sterile/pharma processes for what they sell to their customers. Well, except for the Medspas, those are just wild west snake oil farms.
Today ... who knows? It might just be the same gray market stuff us plebes can get.
They did not make the peptides. They sourced them from China.
Also, if you plan to be on it a good long time, you can buy a bunch of kits yourself (a kit is 10 vials), run a bunch of tests, and then just have a nice stockpile that will last you years. The testing will likely cost as much or more than the product itself, but given how inexpensive the product is, you still come out way ahead financially.
It is illegal, but it doesn't stop people from doing it. In fact, if you don't have any sort of test results for your peptides people will absolutely avoid buying your wares until you have them. Purity and mg/ml are the 2 basic test results that any shop worth their stuff will have.
After nearly getting hosed in a group buy (I did get refunded, but that is far from a guarantee) because of a product mismatch, I decided to just pay for nexaph. Love him or hate him, his popularity relies on his reputation and he has been more careful than most suppliers to cultivate it with more extensive testing and quality control.
<Insert that "one of us, one of us..." GIF here>
I know a bunch of people with multi-year stockpiles. I've got ~5 years of reta and ~6 years of tirz. This is too much, of course, but I determined a while back that under no circumstances do I ever intend to find myself unable to source it. My life is immeasurably better after losing 110 pounds.