I see, that's a relieve i think i buy too much diamonds, so i was thinking of buying some pets or armours to sell for gold, but i'm not sure how to, or should i ask what someone want from the item shop, buy it , send it to it and then that person pays me in gold, or may be the other way around would work better, i don't want someone to scam me >.<U but i'm really not sure how to do it

, er...And other question, please, do i have to make a thread about it on the market place or should i just make a shout (i believe its how its call, sorry my english is not perfect, please forgive me >.<) on the game?
I hope I'm not misunderstanding your question... you're asking how to "sell" diamonds, I believe? If that's the case, it's done quite frequently. Your "buyer" will tell you what object they want from the Item Shop, you select it, click on the Gift icon, enter their name in the box that opens up then send it. They should either have sent you the agreed upon price for your diamonds, i.e., 20,000 gold per diamond (which would be the diamond cost of the object they chose x 20,000 - or whatever your price is). One catch is that you can Gift only one item at a time so if someone wants, for example, 2 stacks of Transport Runes you would have to send each separately. There's not multiple purchase choice available on Gifting.
Another caution, be very sure of who you're selling to. 99.99% of the folks playing here are scrupulously honest but there are dishonest ones out there who will try to cheat you. So, just be careful... if you're selling to someone you do not know my suggestion would be to get at least 1/2 of the gold upfront, if not all of it.
Most people choose to do a World shout that they are selling x-amount of diamonds for x-amount of gold per diamond. This has the broadest reach.
What you cannot do is pre-buy items then try to sell them... Item Shop items come to you Bound... at least I haven't run into any unbound ones in the 2+ years I've been playing. That said, some things can be Unbound... like Wings, which you usually find in the Ruby Shop. By the way, you can sell Rubies in the same manner you sell Diamonds.
Good luck and, if you're in a Guild, it wouldn't hurt to ask your mates about anyone who wants to buy from you... people who have been here for some time are pretty familiar with anyone who is NOT to be trusted. Have fun!