Stanford’s Guidelines to Web Credibility:
Use restraint with any promotional content (e.g., ads, offers).
If possible, avoid having ads on your site. If you must have ads, clearly distinguish the sponsored content from your own. Avoid pop-up ads, unless you don’t mind annoying users and losing credibility. As for writing style, try to be clear, direct, and sincere.
Let’s set the distinction here between commercial sites and informational sites. Ads on informational sites and blogs are fine and a great way to create an additional source of income. Of course, this only goes so far. Even informational sites can lose their credibility if you have too many ads or utilize annoying popup/popunder windows.
On commercial sites, displaying ads that sell similar or competing products/services or directs visitors elsewhere to get what they came looking for, is just plain silly and a bad marketing strategy. You might get a small stream of “additional” income from these ads, but undoubtedly it will be at your own expense in the long run.
Commercial sites should be focused on selling one thing… your own products or services. Anything on the site that pulls visitors away or interferes with that selling process is a bad marketing strategy that will inhibit your own ability to “sell” your visitors on what you offer.
When writing content for your site, be sure to keep your target audience in mind. If you customers are more technologically savvy or highly educated, then write accordingly. If your audience is the average John or Jane Doe Consumer, then write toward them. Whatever you do, don’t write above your audiences head, and don’t talk down to them either. While you won’t be able to please everybody, knowing your primary target audience will ensure that you are not insulting the larger percentage of your audience.
You also want to be clear about what you offer. Don’t write to try and keep your visitors in suspense about what your product or service is. If it’s appropriate, you can use sales jargon that enhances the anticipation, but don’t string it out for too long otherwise your visitors will tire of seeking the payoff and go look for your product or service somewhere else.
The best sites are those that are informative, professional and don’t resort to gimmicky content or designs. The bottom line is that you should treat your visitors as you would want to be treated.