I have wasted a lot money on this

Not sure if I understand your question but I'm thinking your asking about how to get a better price from the items you purchase from merchants. Well, I think most merchants decide how much to charge you depending on your reputation level and maybe alignment. Or maybe some charge you less for completing a quest. For example, Bernard at the Copper Coronet will let you buy his items for a discount after you helped out Hendak. In my opinion, I think ALL the merchants are bunch of capitalist, charging the standard 3 times purchase value of an item. Here's my scheme when I start a game. I would CLUA in a Bag of Holding or "bag31" and then EVERY item that I come across (via battles, pickpocketing, finding, etc) I put those in the bag and then sell most items (except the goodies). Its tedious work but I'm a VERY rich man.

if you mean how to recharge an item, you need to sell it, then buy it back from them. voila, its recharged. if you do it with the wands that you get in irenicus's dungeon, you will have fifty charges in each. i only keep the monster summoning, and cloudkill one. sometimes the lighting or fire, just because no smart mage would be without a wand of some sort, lol.

Something I noticed when I was selling items, is you never get what their worth, however their is one place in the game where you can get double the gold for your items than anywhere else. Good old Shaughin City, under the water. Your crappy basic items are worth a fortune down here I think due to the fact that these folks don't get out much and your stuff is treated as exotic.

with high enough charisma and reputation, you can actually sell items for more money than you buy them for! it's very nice with 9th level spell scrolls, wands with 50 charges, and super-duper-awesome-Hackmaster+90 weapons. it's very nice.