For the most part reinforcing what was already said:1. Discuss this with the players out of game. If in your game world, Lawful means no breaking any laws then make sure the players understand that. If Good means only with a "good" reason, make sure the players understand what some of those reasons could be.
2. In game, have the authorities outlaw them. In traditional societies, an outlaw can be cheated, enslaved, tortured, maimed, and/or killed without recourse. The outlaw is literally outside of the law. This ruins the character's reputation and standing within that society and it taint's the character's family as well. The local authorities may declare that anyone who does business with an outlaw will be punnished. The local church may excommunicate (cast out of the religious community) the outlaws thus denying them all benefits of that religion (goodbye cleric spells, and cleric & paladin supernatural & spell-like abilities). Word will spread from town to town and various crimes will be ascribed to them regardless of their actual guilt (this is how notorious repuations grow). If their transgressions are great enough, the local clergy may preach against them and/or curse them. And finally bounties may be placed on their heads.
Many times in D&D we forget that the PCs are celebrities and that word of their exploits (good or bad) spread from town to town.
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