Ask them to draft up a business plan, including target segment, competitive analysis, pricing model, market penetration forecasts, customer acquisition strategi

Ask them to draft up a business plan, including target segment, competitive analysis, pricing model, market penetration forecasts, customer acquisition strategies, marketing plan, funding requirements, etc. Lay out specifically what you're looking for so that it gets them thinking about the real problems that need to be solved. Basically, unless they can make a substantial contribution to the execution of their idea, it's not worth 50%, or even 1%. 99% of the time, they'll either refuse, defer, or forget about it in a few days. The other 1% are demonstrating their willingness to put in work, and now you have a document that demonstrates their level of competence, and a launch point to discuss the viability of the venture and revenue split.