Well it is unfortunate that there are people who like to cheat others ... I have always said "a favor is not needed just once, you will need that person", that is to say that in some other occasion that person goes to need Some favor from you, that person will already have the doors closed by swindler, I like the last sentence and had not thought about it, I know how much your neighbor is worth ... I applaud this phrase and I liked it:

I lost four dollars and found out what my neighbor is worth.