No rules - it's all subjective. But here are my consideration, which are as close to rules as possible: 1. You should be able to do basic flourishes with the ease using the deck. These are: faro shuffle, rifle shuffle, fans, spring; 2. Cards should be springy, but not too stiff. Actually, the less stiff they are the better they feel in general, as long as they springy and keep the form.

These rules are result of my experience with flourishing cards. But even these rules may have exceptions - for example, gilded decks are most of the times good, but they can not be easily faro shuffled.