Your mistake is to assume that the direct input costs (other than your efforts) are the only meaningful component of the price charged. That fits with your feeling that charging more is "taking advantage of the buyer's ignorance of the original price".
What really happens when you invest your time and labor is different from the cost of the materials plus "a little extra":
1. What is the value of the product?
This is the biggest one. If you create a product that gives me $X's worth of enjoyment, or saves me $X's worth of time or effort, then I should value it at about $X (whether or not that's what I'm willing to pay is more complicated, but the value proposition is simple). If you charge less than that, then I get all the value plus the surplus. If you are running a store, the value you add is choosing items to offer, ordering them, stocking them, bearing the costs until goods are sold, and providing assistance and service to customers.
There is no particular reason that all of that surplus should go to the buyer, and none to you. It's not about what the material components of the thing are, it's what value the thing produces for me that determines the price. There are definitely situations where you can gouge people (charging more than the input costs plus added value, charging prices that are ruinously high for consumers when there are lower prices that are still profitable, and more), but those are not automatically in effect.
Example: I like video games, and my standard for value is roughly $1/hour or entertainment. So my heuristic for buying a specific title at a given price is "do I think I'll get X hours' worth of fun out of a game priced at $X?". I don't care very much about the profits of the company that made the game, I care about what I get out of the transaction.
2. What is your time worth?
Without you to convert raw materials into a product, those raw materials would stay as they are. (1) above covers the value added by making a product out of the materials, and out of that added value you get compensated for your time and effort. If you add enough value that you can reap a larger profit, it's not automatically "unfair" for you to actually do so.
Remember that the time and effort you put into something is time and effort you can't put into anything else, and so it's not unreasonable to want at least as much in compensation for the next-most-valuable investment of your time and effort you could make.
3. You might not be the best judge of value.
This especially applies when working for a company that is run by other people. The decision-makers (ideally) have a good idea what value you add, how rare your skills are, and what they'll need to offer in compensation to keep you from working somewhere else. It's not always as easy to see how your efforts pay off in the bigger picture of the company's overall operations. If your employer is comfortable paying you $65k, then they feel that your work is worth at least that much to them. So let them pay you what you're worth!
As in (1), there is no reason that all of any surplus value needs to go the other party.