Would these methods work for like other stains on the back seat if you catch my drift ??
yea, this method would. However some of the chemicals in certain products related to this can actually bleach the fabric a little. Way i see it is its a car, it lives outside and some rubbish is going to get in it at somepoint.
If you want to be good to it just use one of the hire-able carpet machines that you see and shampoo the seats and carpets with that. Makes them as new.