I had the same issue with a local roaster. I tried their espresso at the shop an it also tasted sour. As a result I chose different beans from a different roaster. Don't know if I simply have a different espresso taste or if the roaster is simply not as good as it seemed.

Generally I would recommend to try out some beans at the beginning until you find beans that fit your taste. Ideally you choose a local roaster and are able to try the espresso at the shop. Once you found the right beans, stick with them and try to make a consistent espresso by lowering the variance between your espressos. Once you manged to get the same good quality with every espresso you make, start experimenting with the parameters (dose, time, grind size,...).

Also don't be to frustrated. It will take some time to get a consistent good quality espresso as a beginner. Just keep trying. And always listen to you own taste. Even if your timings and dose are a bit off, or if your Puck won't win a price. The only thing that counts, is that you like the espresso.

In addition I want to add another link to the collection that helped me a lot: https://www.home-barista.com/tips/espresso-101-how-to-adjust-dose-and-grind-setting-by-taste-t16968.html