If your giving away things to be sold, it basically means that you are giving the item to another person to sell, which means you will be charged for labor. The seller will charge you interest, for example 5% a day. In order to make a profit, you must first calculate the price you obtained the item for. For example $5. Now you must come up with a price to sell it with, that will give you a profit, and cover the costs of labor, without going under $5. In order to do that. You must first discuss with the merchant in which you are asking to sell a percentage of the item price to sell the item. A reasonable % would be 20% with a 0.5% interest on his part for every day the item does not get sold. Now you must incorporate the 20% into your 5$, which is adding $1. Therefore the item must be sold for $6 in order to not lose money. Now you must estimate the money you will receive from interest by guessing the amount of days the item will be sold. Now hopefully your selling a hard to sell item while using a stupid guy because now you're gonna get the money of labor back before he sells it. Perhaps the time is 2 days, which returns 1% of the $1, or 1 cent. That will mean the item will sell for $6.00, and you will use $99 cents to spend on labor (incl. interest), and then acknowledging the $5 you used to purchase the item. Therefore giving you a profit of $0.01. Obviously that is a very tiny amount of money to make, which is where you can experiment with different ratios and percents to find what's best for you. Make sure to rip people off with a price that doesn't seem too much. I mean if you got the item for free, sell it for 20 bucks. If your doing it for fun, well don't even bother, just give it away, be nice. Hope this helps you!
This is common knowledge from my brain.