Hopefully should be cleaning my interior this week. I'll update if i have better results with the bissel.
What kind of seats do you have and what condition are they in? If they are cloth and lightly soiled use a good interior cleaner, like Daks suggestion of Sonax. I use
Optimum Carpet and Interior cleaner. That you can dilute up to 3:1 for light to medium soil. I had a few cars that I had to resort to APC full strength, mostly soccer mom's minivans.
The only time I use an extractor is when the fabric is soiled through, like liquid stains. I still pretreat the seat with the interior cleaner and a brush, then using as hot water as I can get, I use the extractor to do a one pass spraying and vacuuming the water as I go. I don't use the brush on the extractor, too stiff for car seats.
For vinyl and leather,
this brush is the best.
If you have a rotary polisher (Harbor Freights cheap one will work great) a wool pad on it works wonders on interiors. Just make sure you run it on high against a spur or something to get rid of all the lose fabric on it.