Do not open on Saturdays, this is when the homeowners and hobbyists are out and about. If the locals know you are open you will get a never ending stream of broken bicycle parts, broken $19.00 beach chairs, door handles, broken wrought and cast iron patio furniture, kitchen appliance parts, truck ladder racks, car roof top kayak and bicycle racks, home plumbing fixtures, fireplace grates and guards, lawn sprinklers, lawn mowers, floor lamps, reclining chairs, BBQ grills, ceiling fans, floor fans, garage door opener components and so on, most all of these people want you to make a part to repair something that they bought simply for it's low price, you can not do so. Just Say No
Then the dreaded hobbyists begin to show up, the local classic (not wealthy) muscle car guys are the worst of this lot, they will expect you to share their own love of 1971 Chevy Camaros, they will want a new alternator bracket made for instance and will go stark raving mad when you tell them that it will cost in excess of $500.00 and tell you that GM sold them for $14.95 when in production 50 years ago.
Then the motorcycle types turn up, most of the young ones spend a good deal of time on the internet and know all about how factory racing motorcycles are made (-: They will ask for a price on a part using all of the advertising key words used in the hobby world, Aircraft Grade Aluminum, CNC Machined, Hard Anodized a certain color, a generous radius in all corners for appearance only, most of these people also have no disposable income.
The same applies to boat owners, cyclists and RC modelers whether it is cars, boats, rockets, planes or robot vacuum cleaners. If indeed you can become well known in one of the hobby industries you may make some cash, this is tough sledding however.
If you can design and produce a proprietary product that people will actually buy in sufficient numbers to make a profit have at it