One of the first things I learned when I was teaching was that many (if not most) Thais automatically think two things about every non-Asian foreigner: 1) We're rich, and 2) We're Christian.  As my curious students pounded me with questions, I was always amused to see their confused looks when I told them the truth, shattering the preconceptions that they picked up from their parents, friends, or very, very silly Thai television shows.  I proudly told them that I am closer to Buddhism than anything else and am most certainly very, very far away from being rich.  However, the stereotype still persists, and is probably a large reason for the existence of double pricing in Thailand, a practice so outrageously illegal in North America that visitors are nearly always shocked/offended/angered/saddened to see it at nearly every tourist destination they visit.  Essentially, you have two choices: 1) Deal with it and enjoy your vacation, or 2) Get flustered, angry and upset and let it ruin your day.The concept behind it is quite simple actually - you pay more to see things than Thais do.  The reasoning behind it is, in itself, fairly simple, but it opens a whole can of worms regarding principle, ignorance, greed and fairness.

Essentially, the thinking is that, since most farang do, actually, make more than the average Thai, we can afford the extra expense.  On one hand, you're only out $3 or $4 at most (usually less), but on the other, it's still pretty hard to know that you're paying up to ten times what a Thai would pay for the same thing.  For example, a visit to any national park within Thailand costs 80 baht for a Thai, but 400 baht for anyone else.  One thing that makes it even more lamentable is that the lower admission prices are printed only in Thai; many times, a visitor has no idea what's just happened.

Personally, I think it's pretty shameful.  It's a perverse little fantasy of mine to see the reaction if a Thai national visited say, the Louvre,  and was told that the entrance fee for him was 80 euros instead of the 8 that everyone else pays.  "Well, sir, you can afford international travel, visiting one of the most expensive cities on Earth.  Obviously you're quite well-off and can afford this."  You'd have protests outside of the French embassy before you could say 'croissant'.

At any rate, the best thing to do is vote with your dollars.  Do some research online and make sure the places you want to see are worth it.  If they are, consider the extra few bucks part of the cost of seeing the only planet you'll ever know.  If not, skip them and move on to the next one - Thailand has lots to choose from.