How do you go about selling unpopular ideas to people?

In general, people like to hear proof and facts. In this case where you want to sell an unpopular idea to a 'prospective' buyer, you have to address it with positive facts and proof why it will work. You keep the same 'unpopular' concept but 'dress' it / 'present' it in a totally different way that it doesn't look the same as the original concept but in real fact it is. Make them see something that isn't there or could be there. -- Thanks for the invite!

- Believe in it and show that with enthusiasm 

- Focus on the benefits

- Address the right people

- Be smart, make it SMART

Agree with Mr. Devesh

By explaining why certain things are necessary. They won't agree but with time will understand and feel free to ask questions about it

That's the job of a typical sales person..........

By stating that its unpopular because few can realise its merit and realise the idea properly, eg opening a non veg store at a place with high vegetarian footfall is an unpopular idea but for those interested in seasonal earnings at a premium it works.secondly, it is possible the idea is unpopular because few want to maintain monopoly in the segment and so have successfully marketed it as unsuccessful. Thirdly, the idea is genuinely unpopular due to previous failures, but I would sell such an idea only after thorough assessment and clear evaluation that its implementation is possible and being unpopular, competition would be low.

Show the functional and emotional benefit of implementing that idea. Give them a step by step guide for implementing the changes so that it doesn't look abrupt.

To make an unpopular idea, product or services popular to the prospect is the basic work of a sales man. 

Make the decision only for the right cause.  Popularize it only among the target audience by Demonstration, Visual Presentation, Contents and coverage in the form of a Popular news in a magazine that is well received by the target audience and other cost effective methods.

(Mobility card: For train travel, purchase essentials like milk and veg-meat, local conveyance payments of taxi fare--for all requirements within in specified areas with those who are participative members with a common clearing adjustment with a card that is rechargeable just like a mobile--it is going to be introduced by a company  with project of Metro Rail in Kochi-Kerala-India-- The card is also proposed to be used in local buses by incorporating many features like auto refill from bank account in the event of the total balance go below a certain level--safety of use protection from many unforeseen events like many)

Agreed with the answers to colleagues

Focus on the positive aspects of the idea and explain why it will eventually benefit everybody. Ideas may be unpopular but their outcomes are often welcomed once people understand better what is being proposed.