Here's a simple lottery game that could be easily verified by anyone.

Create an npub / website where you can bet on red or black.

When a new bitcoin block comes in, mod (%) the hash value by 2.

If the value is 0 = black, 1 = red.

If black wins, they win reds' pot. And vice versa.

Anyone could verify if cheating took place by doing the incredibly simple block height hash % 2.

You could follow this example to make the full game of roulette with other odds (including house wins).

The real question is legality.