Riding Lawn Mowers

I am frustrated ......I purchased a gt52xls to replace another manufacturers tractor......went to a private dealer not the box store.....20 hrs on tractor....would shutoff when pto was engaged..took it in....2 weeks later it was fixed.....I owed them 40.00....for 2 sparkplugs...still under warranty....20hrs. Also purchased the 3 bin bagger for this machine....and when the belt driven motor is attached to the tractor...whether deck flexes into the floor board of the tractor it drives the double stacked pull into the floor cutting a groove in the floor......can I change the spindle on The left side of the deck to the single one on the oposite side.....I have never used the bagger system nor Will I ......I was talked into wasting my money on this too....but also do you think there is a issue with this engine to need the spark plugs changed in 20 hrs.....