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.
One of the most beautiful and exciting qualities about blogging is that you can create a blog that deals with any subject area that you are either knowledgeable or passionate about (and preferably both!). You can write about personal finance, careers, real estate, getting into business, technology, cooking, travel, personal health, or just about any topic you choose.
Provide excellent customer service. Answer any questions buyers post as quickly as possible. Be professional and courteous. Positive communication builds your reputation with buyers and gets you return business. Also, package your product well and ship it out quickly. Allowing an item to become damaged or taking too long to ship can negatively affect your reputation among buyers. Wrap all items, especially fragile ones, in appropriate packaging. Commit to shipping items as soon as you receive payment.
Again, if your blog has a large reader base, then businesses may be interested in paying you to review their services or products. Not only will you get a free trial using whatever these businesses are selling, but you will also get a fee for writing them a review and posting it to your site. Paid reviews (and other paid and sponsored content) can be big money, so advertise this service on your contact page to generate business.
What these opportunities typically turn up to be is a pyramid scheme. You pay a fee to signup. You then receive a flyer saying how great stuffing envelopes is and list of names and addresses to mail said flyer. IF those people pay that signup fee so they can mail that flyer too, you get paid a small referral fee. ONLY if they take the bait do you get paid.