"My wife told me, "Don't do business with Christians. They will cheat you every time."

I'll have to agree with your wife a little. My best friend is kind of a radical Christian (wasn't always) and won't do business with anyone but people who say they are Christians. He takes his vehicles to a local auto repair shop that is owned by a fine upstanding Christian he goes to church with. One time he got a bad oil leak on his truck and took it in for repair to this fine Christian mechanic. The mechanic told him he his oil leak was caused by a cracked exhaust manifold and suggested replacing BOTH exhaust manifolds just to be safe. My friend decided it was way too costly to repair the oil leak and just put a drip pan under his engine. When my friend told me about the cracked exhaust manifold theory I told him his mechanic was a liar and a thief but he didn't believe me. I took a look at his truck and found out the oil pressure sender was leaking. I helped him replace the sending unit and no more oil leak. As far as I know my friend is still using this mechanic because he's a fine Christian.