I got an email from a company offering to sell me lots of keyword rich domain names, saying that it would guarantee me higher rankings and increased traffic for my website. Is this a good idea?
This is a highly deceptive practice that is likely to get you into trouble on the search engines. Any attempt to deceive the search engines will ultimately lead to penalties, and possibly even get your website banned from Google.
Whilst you could forward all requests for your numerous domains via a 301 permanent redirect to your main site, it’s unlikely to be a winning formula for search engine success. More likely it will be an expensive waste of time.
Similarly, if your plan is to create lots of websites for these domain names, you will again get into trouble if the sites simply duplicate the content of your main website. However, if you are able and prepared to offer genuinely unique and valuable content on each of the sites, there’s nothing wrong in that.