I don't think these issues are unique to GM sadly.
I recently test drove a Honda CRV and told the salesperson explicitly not to call me and that we're just test driving and comparing various models for a couple months. He not only sat us down with the 'hard sell' but literally called me every day for 2 months. Note his 'hard sell' was $300 off MSRP.
I feel the independent dealer system has largely failed us and they're all terrible and unfixable. If I end up buying a Tesla it will be less for the car and more for the lack of traditional dealer experiences. Or I end up buying a 3 year old car and enjoy the savings from massive depreciation.