I merchandise occasionally, but it's rarely worth the money (unless, like JAS, you have built a long-standing relationship.) Mostly I take short jobs to fill in time between other shops.
Apartments pay well, especially senior living ones. The real way to make money, though, is to route shop, even if it's just a day route. Start with Apartment 1, pick up some post office shops, gas shops, and bank shops on your way to Apartment 2. Post office and gas shops do not pay a whole lot, but they're simple, easy to report, and make good fillers. In the above scenario, you could potentially make $100 + another $20 or so in gas in 3 or 4 hours (plus reporting time.)
"Let me offer you my definition of social justice: I keep what I earn and you keep what you earn. Do you disagree? Well then tell me how much of what I earn belongs to you - and why?” ~Walter Williams