I have been using Social Spark on my other blogs for quite some time and it accounts for about 50% of my monthly revenue per site. You can juggle the battle between reader loyalty and earning revenue by keeping your sponsored posts to a minimum. About 2 sponsored posts a month is enough to help with revenue without losing your faithful readers.
How It Works:
Social Spark offers you leads from companies wishing to sponsor posts, which you can accept or decline. Once you accept a lead, the company will then review your blog and decide if they want you to advertise for them. If they accept your blog for a sponsored post, you have the opportunity to accept the amount they offer or negotiate a price that better suits your needs. Blogs with higher traffic can usually negotiate higher prices. I've seen lead offers be as low as $5 and as high as $200+ for a single post.
Each lead will have requirements for your post. They usually require a certain word count, a dofollow link to their website, an image, and a positive review of their product.
To add a little extra help in the revenue department, they also offer referral commissions at the starting rate of 5% of everything your referral makes from Social Spark. This commission stays active for the duration of your referral's account. Once you refer at least 5 people, your commission jumps to 7.5% and gradually increases to 15% after 50 referrals. 5-15% may not sound like much until you consider the fact that I make an average of $50 commissions from my referrals each month and I don't have to do anything now to earn it. I could shut down all of my blogs and never get online again for the rest of my life, and still be earning monthly commissions from my referrals. See how I get my Social Spark referrals HERE
Payments are made via Paypal and you can cash out when you have $50 or more without penalty. Anyone wanting to cash out an amount under $50 is subject to a $2 fee.