There are numerous printing companies that will print your designs onto not just T-shirts, but also hoodies, hats, posters, cushions, bags, and phone cases, to name a few items. These businesses also offer fulfillment services. This means that you promote the merchandise on your own site and once you sell a product the printing company will not only print your design but also send the item directly to the buyer. So all you have to do is concentrate on the marketing and selling of your products, and the fulfillment company will take care of the rest.
Affiliate marketing is also called "performance marketing", in reference to how sales employees are typically being compensated. Such employees are typically paid a commission for each sale they close, and sometimes are paid performance incentives for exceeding objectives. Affiliates are not employed by the advertiser whose products or services they promote, but the compensation models applied to affiliate marketing are very similar to the ones used for people in the advertisers' internal sales department.
Decluttr is easy to use. Grab an unwanted item, check that Decluttr buys it (for instance: CDs are great, old clothing is not), and enter its barcode into Decluttr’s “valuation engine” or use your Decluttr smartphone app (iOS and Android) to scan your item directly. You’ll receive an instant price quote that you can accept or decline with no obligation. If you accept, just pack your items into a box large enough to fit them, slap a free Decluttr shipping label on it, and bring it to any authorized UPS location (including drop boxes, if your box contains fewer than 25 items). Decluttr issues your payment the day after your item arrives by PayPal, direct deposit, or paper check. There’s no practical limit to the number of items you can sell: each order is technically limited to 500 items, but you can create as many orders as you like in any given timeframe.
If you have a good idea for an app, and the skills to create it, then producing your own premium app can be profitable. However, with so many free apps available, it may be hard to convince people to pay. If you want to go down the premium app route, consider having a basic free version to encourage people to download the app in the first place. You can then provide the option of upgrading to a premium plan once users realize how useful the app is.