Lots of major websites have set up marketplaces, as well as classified listings, once they've built a large community. One high profile example of a blog doing this was with Mashable, who have now closed their marketplace.

Toms, the socially shoe brand, also launched an online marketplace that showcased products that were 'giving back' to the community.

Advantages: Businesses will often look for large communities that are relevant to their niche, so there's loads of opportunities to sell classified ad space within your blog. As well as this, you may have a lot of opportunities to mention specific ads within your content to further increase revenue potential.

Overall, this can be very profitable if you're generating good levels of traffic to your blog.

Disadvantages: Setting up an online marketplace isn't easy and can come with a lot of headaches. You will need to dedicate a set amount of time each week to be adding/removing/updating new listings as well as actively promoting your marketplace.

Even after all this, you may still struggle to get uptake on your ads and you could also risk making your site look overly-commercial.