Research selling prices of items similar to yours. Look up completed sales or current listings of items similar to yours. Find the high- and low-end prices, and price your object around the median price level. If you want your item to sell quickly, price it at the low end. The condition of the item also affects the price. Items in poorer condition should be priced at the lower end. Also, consider how many listings there already are of items similar to yours. If many similar items will be competing with yours, you may have to set the price lower to get the sale.
Upwork: This website offers a great marketplace for selling just about any professional service. You don't need a merchant account, website of your own or anything else for that matter. All you need to do is be able to provide a high-quality service at a reasonable price. But be informed, you will have to compete with many others that are constantly bidding on open jobs.
most of these site you have to be older then 18, so thus you couldn’t do any of them unless in your parents name, also you would need their credit card or pay pal account, which i don’t think any parent would let their kid have that account, best advice i can tell you is to try working in lawn care, good for you wanted to start working young, i know how hard it can be living in a small town with poor parents, mabye ask around for idea, beware of the net though, net jobs are mostly scams and they onces that aren’t you mostly have to be 18, mabye if you don’t need a permit in your town sell cookies, or your old toys in a yard sale. cleaning jobs, are good. good luck, i know what it like being you, work hard