That's definitely hard. However, I did see people sharing their screenshots of a good multiwin, it's too rare though. But, I would not be optimistic about it, it would be better if you would expect nothing that came from a free spin.
Heck, even with free money, bonus money, weekly rewards, and monthly rewards, I don't expect too much from them. It's those who are depositing money who are most likely to encounter a max win or good rewards and I think it's part of the system where those tips and bonuses including the free spins have a lower chance of winning than it is with deposited money.
Just a very good example that we have here in the forum, the freebitco's Wheel of Fortune. The highest rewards that I have seen based from the players here were like 1400 RPs or 1400 Lottery tickets. Long ago, I believe I got like 15k satoshis about couple of times. They vary the numbers depending on the the current rate of btc in the market. However, I haven't seen or read anyone saying they got the watch or the phone from spinning this wheel. So I would surmise that it is indeed rare to see someone win the top prizes in spinning a wheel, even if it is a paid one or need to buy or wager something to get a free spin.
And maybe, for those who got really good prizes, they are not here in this forum to talk about it. How many rounds we have seen this win a lambo contest, and yet, no one here announced he was one of those lucky winners? So I am assuming, most if not all are not part of this forum.