Relying on a salesperson to choose the best car for you, instead of doing your own homework, is possibly the worst kind of car-buying rip-off and there's no-one to blame but yourself.
While a good salesperson can help you select from what's available at her dealership, you can't expect her to tell you that a competing product is superior or more suited to you. That's not her job.
It's up to you to honestly assess your needs, read the reviews and test drive a few cars to make your selection. If you've done all that and still end up with a dud, then maybe you can blame a salesperson if it makes you feel better.