Its a moral question.. joe is not honest. Bob is new in

Its a moral question.. joe is not honest. Bob is new in town.asks about joe .. do you tell him joe is a crook or do you say.be careful ..like all plp becareful
Bob loses money .he says why didnt you warn me ...you tell bob.."i said be careful.."" bob says ..no !!!!!! you should of said ..do not deal with him..!!!!!!

which way is correct way???????