I bought cheap clothes and replaced the expensive clothes the townspeople were wearing, and sold the expensive clothes. Trading a collared shirt for a screen printed tee shirt brings a profit of $300+.
On the other hand, if you like the cute outfits in the store, you may as well put them on the townspeople, because they're there forever, unlike the temporary mayor. I do switch my mayor to a cheap nightgown or jammies just before retirement, the one piece for 129 coins is cheaper than a whole outfit.
Also, only buy apple trees, because you can get golden apples. I've had as many as three in one day. There is no advantage to orange and pear trees, and the pears are really hard to see against the grass.