Secrets

Easy Money
Due to the simplicity of the in-game economics, anybody with a decent Guile score (around 3 or so) and a half an ounce of patience will be able to buy anything in half an hour.

The easiest target for this cheat is the guy in Bowerstone South right next to the entrance. Buy out all of his potions (health, will and resurection philes). The more of these items you have, the faster you make money. About 25 of each (except res. philes, you can only have 9 of them) is the best to start with. Since the price of each item is based on how many the vendor has in stock, when he has none, he'll pay a fortune and when he has a lot, he'll sell them cheap. You don't even have to stop talking to him. Just make sure that when you sell, you hit the sell all button because selling in chunks drops his buying price. Once you've sold them all, buy them back all at once at his reduced price and repeat the process.

I discovered this cheat with a little over 9,000 gold earned the hard way, and in 10 minutes I had 100,000 gold. I then visited every shop I could find, bought the store out of their potions (wound up with about 230 health and will) and in another 10 minutes of exploitation, I had 700,000 gold. If you can get a bunch of wedding rings, you can speed up your profit level even faster with that same shmoe in bowerstone south.

Sleep in already occupied houses without the fine
Don't do this trick if the house's bed is too far away from the entrance. First find a bed in a house and then try to sleep in it. It'll warn you about it but click yes anyways. Then quickly run out of the house before the screen fades and you won't get a fine from it. The game thinks you slept, but there's no intrusion of property fine.

Glitches

Hero Save Exploit
In the middle of a quest, if you use a hero save and reload the save, you will start at the beginning of the quest as if you had never begun, and you will retain all items that you obtained during the last run of the quest. This is especially useful in the Arena, where vast amounts of money can be made if used right. This exploit can also be used to get infinite silver keys, potions, etc if used during missions. If used too many times, this exploit can cause damage to your saved game.

Infinite Silver Keys
Normally, Silver Keys don't duplicate. After you get one, that one is gone from the map. However, you can get as many as you could need during the "Save the Archaeologist" quest by using the Hero Save exploit.

During the "Save the Archeologist" quest, fish in the pond across from the Demon Door and get the Silver Key. Save your hero. Now load the game you just saved. The Silver Key you fished up is still in your inventory. Go back to the pond and fish again for another Silver Key. Continue this process to get all the Silver Keys you'll ever need.