I've heard people say it's wrong to read anything besides the King James Version. However, it's a little difficult to understand. Are the different versions different enough to where I should be concerned? I did read one verse about peddling God's word (KJV said corrupting, which is a lot different than peddling, IMO). Are there a lot of issues like this?
I read multiple translations at the same time. If I feel uncomfortable about any differences I come across, I can look into it to see what's going on. The 2 Cor 2:17 corrupt/peddle conflict you noticed is a great example.
I quickly looked into the corrupt/peddle thing, and here's what I found. The word in question here is the Greek word kapēleuō. I'm no expert in ancient languages, and this is actually a tough word, because this verse is the only time it's used in the whole Bible. So we don't have a lot of context for its usage.
The dictionary (Strong's) definition of the word is:
From kapēlos (a huckster); to retail, that is, (by implication) to adulterate (figuratively): - corrupt.
So both translations are, technically, correct.
The KJV translation accurately translates what the word implies, but leaves out the "profit/sell/retail" element, which is the literal definition of the word. It's not
necessarily monetary profit, though, the implication is just some form of personal gain.
The NIV translation, technically, accurately translates the word, but the "corruption" element is absent, which also seems to be part of the connotation of that word. The NIV also
feels like the implication is monetary profit, which is not
necessarily what this word must exclusively mean, although it could easily be used that way.
So this is a really good example of why I read multiple translations: both translations are technically accurate, but reading them together gives you the most complete understanding of the word.
Interesting side note:
In this case, The New Living Translation (surprise!) seems to give a more complete rendering than either of the above translations, as it implies the "trickery/corruption" concept as well as includes the "profit" concept:
"You see, we are not like the many hucksters who preach for personal profit."
Also, here is Thayer's definition of the word for your consideration (note 2c1 especially):
1) to be a retailer, to peddle
2) to make money by selling anything
2a) to get sordid gain by dealing in anything, to do a thing for base gain
2b) to trade in the word of God
2b1) to try to get base gain by teaching divine truth
2c) to corrupt, to adulterate
2c1) peddlers were in the habit of adulterating their commodities for the sake of gain