How many psychologists does it take to change a light bulb? None, the light bulb has to want to change. So the joke goes. However, it's possible that the light bulb could be persuaded to change. Persuading people to buy online (from TVs to groceries, holidays to services) can be achieved with techniques that marketers and psychologists have known for years.

Persuasion isn't rocket science; it involves understanding aspects of human nature that are often automatic and work at a subconscious level. Here are 7 ethical ways to persuade people.

4. Persuade with pictures & videos

Imagery is a very persuasive tool in increasing product sales especially for high value and luxury goods, so be sure to provide good quality images of products. They go a long way to reassure people about what they'll be getting.

Images should:

• Be of professional quality
• Offer different views
• Be enlargeable
• Show scale and context of use

Oli, which sells clothing online, has gone a step further. They have 15 second video clips of models wearing the clothing, walking down a catwalk enabling you to get a better feel for how a product looks and moves. With increased bandwidths, this may be the future for some types of sites. Watching videos requires less effort than reading and offers a richer experience - be sure to give users the choice and not to start videos automatically.

5. Cross- and up-sell

The person that suggested "Hey, why don't we ask customers if they want fries with that?" was on to something big. Once people have committed to a purchase, persuading them to buy more becomes easier as one foot is already in the door. The same applies online too.

Don't underestimate the potential profits to be had by up- and cross-selling. Display related items and extras near products like they do in real stores. This will make it quicker and easier for people to buy more items. If you browse for bagels on Ocado, for example, they also show you cream cheese and when you checkout they display any offers you missed out on - a clever tactic to persuade you to buy more.

6. Show authority

The principle of authority states that we're more easily persuaded by those with authority. If Tiger Woods gave you advice on your golf swing, you'd be more inclined to follow it compared to the same advice from your mate, Bob. Likewise, websites showing authority and expertise are trusted more. This is particularly important for B2B sites.

You can show authority by:

• Showing you're an expert
• Backing up facts with links to 3rd party sites
• Referencing governing & authoritative bodies
• Displaying symbols and imagery of authority e.g. VERITAS, padlocks for security

7. Allay people's fears

What if I need to return items? Are there any hidden costs involved? These are the sorts of fears web visitors may have and you need to reduce them if you want to persuade people to do business with you. Answering their concerns upfront and quickly will positively influence people and lower their fears.

Conclusion

Persuasion in its simplest form means giving users the information they need to make an informed choice, helping them to trust you and allaying any concerns they have. It's not about manipulation. Always remember, these persuasive tactics will only get you so far - your site still needs to provide a good service and be highly usable to guarantee success.

This article was written by Lisa Halabi. Lisa's crazy about usability - so crazy that she works for Webcredible, an industry leading user experience consultancy. When not developing information architecture she can often be found doing interaction design.