Quickest way (besides spending $$

) is Tom. Send him out for expensive things (jewelry) and sell it full price. Are you close to 40, diamond rings make a lot. You can even make more money on most truck orders than full price.
Finding cheap stuff in the paper and reselling it. I see cheap milk, sweaters, popcorns and pies ALL the time. Occasionally other good stuff too. When I find someone selling a lot of really cheap things I follow them. I've scored big time checking in on those farms every once in awhile.
Have a lot of trees and bushes (if you have the axes and saws to chop them down) sell them full price. Not the quickest way, but it is a nice income.
Normally I'd say sell everything in your stall, but unless you are still really behind in your machines at your level I'd save some stuff for orders. I get plenty orders that give good xp and money.
gc: kewb lvl 57 I'm a proud F.A.R.M. member