Don't allow room for mistake when you make an agreement
This is very common when you don't have negotiation skills. You can end up falling for a trap without you even understanding and will be your fall. If you are making a trip and the person gives you a price always ask if is per person or everyone. If you gonna make an activity once again ask if the price is per person and ask if the price is per hour (example: some workshop about painting). You should always keep in mind that you can get tricked really easily if you don't make the right questions.