Millions, apparently, so if you’re not an established brand, you’d better learn to spell.
That’s the message from research done in the UK, which claims that “a single spelling mistake can cut online sales in half,” presumably because of consumer concerns about a website’s credibility.
The BBC article seems to be based on testing of a single website, so I wouldn’t go building a a business around the news. In general, I would think that there would have to be more negative cues pushing visitors into the “do not trust” mindset than just typos.
But short of being a known entity with a well-recognized brand, you really have to pay attention to the details, like typos, that audiences register consciously and unconsciously. Even without a dedicated budget for A/B testing and on-going usability evaluations, you can develop checklists for new content that help ensure consistency of message and that eliminate the sloppiness that raises eyebrows in your audience.