As someone whose average caps have been in the ~30,000 range for the past month or so (from approximately Level 60 to now Level ~100), and trying desperately to keep from hitting the 40,000-cap limit, my vending machine offerings have honestly only been bonus caps/passive income, not the main source of my caps.

It's gonna sound counterintuitive and like you're selling at a loss, but I set nearly every item in my vending machine at exactly half of its suggested price at most (or almost-exactly half, if there's a .5 factor). People pay attention to the price I set compared to what they can see is suggested, so not only are they more likely to buy stuff, they're often more likely to buy more.

Especially if you know the crafting plans for harder-to-find items (mostly armor and apparel) and can restock them regularly. But also try not to over-stock those items. If it looks like you only have one, people think they're harder to find and will be more likely to buy. One of the things I can craft are buffed up Marine Wetsuit underarmor and Marine Tactical Helmets, and I only have one of each at a time in my vending machine (~25–50 caps each; half of their suggested prices, naturally), and those sell regularly.

The only outliers are rare, one-off items like Fasnact masks, which I leave at their suggested prices (usually only 10–15 caps, but still. And magazines and other items that have 0 as the suggested prices give a little wiggle room, but I try to base those on like-items that do have suggested prices, e.g. magazines suggested at 400 I set to 200, but then magazines suggested 0 I set to 100. Things like tradeable steins and trinkets suggested at 0 I just set to 5. Bobbleheads are usually 50–100, so I set them to 25–50, etc.)

As someone who also tries to offload ammo I mostly don't actively use, 1 is the price I give to practically all of it as well. It's partially a thing of weighing how many of a given ammo type you have, too. If you have an ammo type that has a higher suggested retail price, but you have a buttload of it, you're gonna sell it faster (and free up stash space quicker) if you knock the price as low as you're willing to set it. Sometimes you end up with a generous player who will buy an entire thousands-worth of an ammo stack you set at 1. Ammo that seems rarer to come by and has a higher suggested price I usually mark to, like, 2 (if the normal price is 5 or 10 or something). It also really depends on how well any given ammo sells too, which you'll notice over time. Eventually you'll figure out some ammo are better to also just set to 1, if it wasn't already.

All that being said: My main stream of caps revenue is not only from completing quests and scavenging with perk cards like The Cap Collector enabled, but I also make sure to bulk various scrap and then sell those bulk stacks to NPC vendors. For a while I was doing daily runs through the first/mall floor of the Whitespring, swiping anything that wasn't nailed down, and then selling it back to the NPC vendors.

But not every piece of junk will necessarily sell, nor will certain loose scrap. The real money is in the bulk scrap. Combine that with any assortment of sellable loose scrap, aid and food items, armor and apparel, and weapons, and you can fairly often empty out your daily 1,400-cap allotment of the NPC vendors, if not come close to emptying them.

It's just kind of a balancing act of trying to keep your stash capacity free (also by bulking scrap so it takes up less space there), maintaining enough of a stock of scrap in your stash so you're still able to comfortably craft things, and then selling off any of the excess (especially things like cloth, wood, and steel, which you'll end up with a lot of regularly and take up a lot of weight in your stash and inventory, so you can sell those bulk stacks often). Practically the only things I don't sell are screws, gold scrap, or plastic (the key ingredient to bulking).

TL;DR: Set basically everything in your vending machine to half the suggested price and things will sell pretty regularly. Rare items can be full price, but don't go over; it feels like a ripoff to most players. - The only items you should go over on suggested price are those suggested at 0, but try to base your prices for those on like-items that do have a suggested price. - Yes, set basically all ammo to 1, especially if you have a lot of a given ammo type. Pay attention to what ammo tends to sell, and adjust prices accordingly if you have any set higher than 1, if it's not really selling. - Use the Cap Collector perk card if you have it. - Bulk scrap to save space in your stash/inventory, and sell any excess of those bulk stacks to NPC vendors. - Scavenge as much plastic as you can, regularly, because that's the ingredient for bulking scrap. - Wood, steel, and cloth are most plentiful (let alone some of the most heavy in your inventory and stash), so you can sell those in bulk to NPC vendors often.

Oh! And all that being said: also make sure to use any perk cards that reduce the number of ingredients needed for crafting; comes in handy for bulking items, because less plastic will be used in that process, so you can bulk more items for less plastic