Guest blogging is a content marketing strategy that consists of someone writing and publishing a blog post on a third party blog to promote themselves, their business or brand. Websites agree to guest blogging especially when the topic or content ads value to their audience. This is usually achieved by going into a specialized topic that isn't fully covered on their own blog that their audience is interested in, or by providing insight and information as an expert in a field.
Guest posting is especially useful for brand building. The main objective is to get the attention of other people's audience that could also be your customer or are in your target market.
In 2012, Ex-googler Matt Cutts explains guest blogging vs. spammy guest blogging for links and using black hat tactics like article spinning. A year later guest blogging vs. paid links was addressed on Google Search Central.
Google's John Mueller recommends adding no-follow attribute to links from guest posts in Google Webmaster Central office-hours hangout on Dec 22, 2017. This was previously expressed as a good practice by Mueller on Google+ (now shutdown) and his Webmaster Central hangout on February 11th 2013 and again on February 25th 2013.
No. This is against Google's guidelines. SEMRush, a popular SEO tool, actually tried launching a service that sold guest blog links.
When SEMRush launched this paid guest blogging service in 2020 it was put under scrutiny by Google and later shut down the service.
That's an unnatural link - the kind the webspam team might take action on. https://t.co/kfQQithCnK & https://t.co/q5GmAxx2YM have more. Making sure the links use rel=nofollow / rel=sponsored would still allow sites to get visibility without having to worry about manual actions.
— 🍌 John 🍌 (@JohnMu) June 3, 2020
Mueller called it an unnatural links scheme and SEMRush removed the service from their website.
Based on SEMRush's guest posting service (now depreciated), a guest post can cost between $225 and $525+ USD, depending on the amount of traffic the site receives.