ThredUP sends you a free Clean Out Kit to fill with all the gently used, on-trend clothes you no longer wear. They'll take care of everything else, including professionally photographing your items and listing them on the site. You receive an upfront payout once the items are processed, or if it's a unique item, you'll be paid once it's sold. Payouts are offered in the form of ThredUP store credit or donation to a cause, or you can transfer the cash to PayPal.
If you’re looking for inspiration, my friend Michelle Schroeder-Gardner of the website Making Sense of Sense has become the expert on all things affiliate marketing. Michelle earns more than $100,000 per month from her blog and the bulk of her income comes from affiliate sales. Michelle has had so much success with affiliate marketing that she even has her own course called Making Sense of Affiliate Marketing.