There is a wealth of evidence that vegetable and seed oils are bad for your health as they are heavily processed and oxidise at high temperatures. Have a read of this article
Commercially bought salad dressings are usually full of bad seed oils and many other nasty chemicals and should be avoided at all costs.
It is so easy to make your own and they taste so much nicer.
All it takes is to combine the ingredients into a container and can be well sealed and shake to emulsify.
1 part balsamic vinegar to 4 parts extra virgin olive oil, salt and pepper
1 part lemon juice to 4 parts extra virgin olive oil, a small handful of toasted flaked almonds, a small handful of chopped fresh mint, salt and pepper
Tangy cider apple vinegar dressing
1 part cider apple vinegar to 4 parts extra virgin olive oil, 1 tsp of dijon mustard, salt and pepper