Hence, all you have to do is check the team, that is what I do and it worked not bad so far, if the team is hard working and actually does anything that means they are good, if the team doesn't really do much other than creating web pages and designs and market their product instead of actually working on it, that means they are bad. Try to stay away from the ones that has the biggest marketing budget, the good ones always have a big development budget instead.
Agree with you, actually we should follow our instinct that dictates by our brain and not our heart, as there is power in mind that will keep us saying the truth, but sometimes the heart denies it and doesn't agree, heart will always say to give chance, but the mind will say the truth that you should beware on it. So, better to ask your mind always not your heart. Anyway, if we really want to be sure, let's always use our mind/common sense.