What does it mean to walk carefully on the gravel road?

This is the comment on writing of a quack fortune teller, which means:

You are in a situation like a horse walking on a stony road. There are many risk factors. You must be careful not to make a decision or take a step easily! Listen to him.

My suggestion is that caution is inevitable. No one can be smooth sailing, even if he doesn't say it. This is the principle of doing things, and it has nothing to do with fortune tellers! He should be cheating you into paying. Be careful!