Most of the bagged salads taste a little artificial because they are treated with a preservative to keep them from browning so fast in the bag. Some people, my dad & DH for example, actually get sick from the preservative. Some people say you can wash the bagged salad with a veggie wash (like Fit) and remove the residual chemical. I haven't tried that, I just buy fresh lettuce.
I work in the restaurant business, and in the places I've worked there has been nothing magic about our salads.
We didn't add anything like salt and pepper or other spices, it was straight lettuce (type varied), spring mix, various veggie toppings, then any optional toppings like bacon, nuts or seeds, croutons or granola, dressings. Some might put some kind of seasoning on, I don't know. The only thing we did do differently is that we always washed our veggies, lettuce included, in a veggie wash.
I had the same problem with home salads for a long time, which was weird since I made them the same was as the restaurant salads, sometimes with ingredients I brought home! It just felt different, I never hit that magic blend of things. Remember, a restaurant salad is typically taste marketed for just the right mix of flavors. Our salads at home are kind of thrown together. Experiment, see what you like, try reproducing a restaurant salad maybe, and see what happens?