Bad service

I bought a car from Nissan Milnerton preowned the salesman was quick to get the deal finalized because month end was approaching the deal was done a few things needed to be sorted out which it wasn't it's now left in my hands to sort out there after service is bad now I wonder why these dealerships don't last, they quick to sell you a car but after that you on your own I wouldn't buy another vehicle through Nissan