Smart gambling is gambling using free money so when you lose you wouldn't feel very bad. Free money from rains and faucet sites and freebies. If you gamble with your own money then there will be no smart gambling, just need to stop at the right time which seems to be very hard to achieve.
That would be so smart to use free money but I guess it's not possible for all of the gamblers, actually when you use free money there is no thrill because you would not mind if you lose anyway. We gamble because we want to fee the thrill and we can only have that if we spend something that is important for us which is our own money, it's okay to lose then but as long as we can afford it.