I bought this basil about a week ago. Seems it always get these dark

Hello! This is a basil disease caused by infected soil splashing on the plant’s leaves. Best to get some new soil and pitch the diseased Smsokl. I would not eat the diseased leaves. Good luck!

I’ve bought organic fancy-schmansy basil in tiny plastic boxes, and the darker spots are on those leaves, too. If you cook fresh basil whole, as on a pizza, brown spots develop. I love basil so much and have never gotten sick from it. Maybe I’m lucky. ☺️

It's called Bacterial Leaf Spot. Bacterial leaf spot is caused by the fungus Pseudomonas cichorii. Symptoms of infection first show as round brown spots on basil leaves. Infection usually occurs when water is splashed on the leaves during warm, humid weather or by unsanitary gardening practices, such using dirty gardening tools.

This is the reason why it's not recommended to refrigerate fresh basil leaves. It's not recommend consuming basil that has turned brown/black, especially if it is "slimy" to the touch. Even though a few brown spots are probably safe, it will be bitter and slimy.

poor drainage in the pot, too heavy a soil and keeping too wet will also cause black spots

https://www.gardeningknowhow.com/edible/herbs/basil/basil-diseases.htm

I would change from the grower your getting them from. Try another store.

You are watering too much. Water less frequently and you will see a difference. Also I noticed from your pix some leaves look as though they have been chewed. Slugs cause this. I would try watering with diluted murphy oil soap. Not sure if this is safe but I used to do it once or twice a season and never got sick.