That's very true too. I hate people who just throw two dogs together for money. They are ruining dogsI think there's also a lot of influence in their breeding too.
My family has owned a number of chihuahuas and even bred a few. There was such a MASSIVE range of personalities etc.
I also pet sat for a chihuahua breeder once, very quickly decided I was never going back there. I believe that was the first time I ever received a genuinely aggressive bite from a dog.
I think when it comes to Chi's not enough care is put into breeding suitable temperaments. Their behaviour is excused too much to the point dogs are being bred that should not be bred.