Open for Business doesn't exactly work that simply. The game has a lot of surprises if you are just thinking all townies can afford everything.
First it depends on your business level. Around level 5 some richer townies will start showing up. Even a few of your own played Sims who may have more money than a homeless townie. But you have to remember AL and M&G makes OFB not play exactly as it did when it was new and very few EPs. You have the AL townies now (if installed) which overrules the base game townie character files and some of the richer NL townies.
Those Sims add flavor to your apartment life experience but very little to the OFB experience as before.
Two NL townies who won't show up at all until about level five or six are Mr. Big and Diva. They have money but more in inventory sometimes than money. They could afford a car, maybe. However, OFB is based on throwing you some curveballs.
For instance, if no EPs are installed except OFB (nor M&G) then Townies who come to cause trouble (hang out, just browse, socialize too much when inventory is low, cause messes, complain about messes) are there to make you realize your prices are too high. :p
You throw the bums out if they don't have any money. Ask to leave. Or lower the prices when townies tell you they can't afford it. If they still don't have money, throw them out. They will cause problems if the stock gets low and they have nothing else to do. They will be replaced by another before your business closes.