Frequently in magic groups on Facebook someone will say they want to sell a trick and want advice. There’s a lot of bad advice (in my opinion) that is then given. One of the things is to go straight to Penguin Magic with the idea, however they usually won’t produce your idea, you’ll need to make it and send it to them. Last time I looked into it, their terms weren’t the most friendly to the creator. You were making product, sending it to them and they would pay you as sold.
A better approach would be to go to Murphy’s Magic and pitch the idea. If they like it and want some of it, they’ll be a couple of options, like you could sell them the idea, they could help you with manufacturing, or you could just sell them the finished product.
Of course by that point you should have done your homework and know how much it costs you per unit to make, and how long it takes you to make them in quantity. Also if you’re self producing, you’ll need to be able to fund making the first batch of your trick as most accounts are on NET 30, so you won’t get paid for a month.
Then you need all of your collateral, so ad copy, art, instructions, etc. Usually you’ll have some of this done before you pitch the idea, but not always. For example my Take Out Box was something that was in my show for a while, so I had tons of video of it that I could pitch it with. Once I had interest, then I went out and started getting all of the other stuff in line.
Personally I’ve made a choice to not mass market thru big magic distributers for most of my products. My reasoning is that going direct thru magic shops I’m able to make more per unit and since I hand make almost everything I sell, it makes more sense to sell a few less units, but make more per unit!