So hi im new using GECK and what i need to know is how i can make NPC do like this: player buy item trough dialogue from NPC (chatting with NPC, not going to bartermenu), then player tries to buy same item again but NPC would say that you already have that item and wont sell more or when renting a room "id like to rent a room" option disappears after renting a room. please help ive been scratching my head for hours because of this >.<

never mind

The easiest way would probably be to just give the player an item like a key, and set your dialog conditions so that the dialog only becomes available after the player has the key in their possession. For example:

Player: I'd like to rent a room.
NPC: OK, sure. That will be 100 caps, and here's your key. (give player key and take 100 caps.)

Later on...

NPC GREETING: Howdy!

Player: I'd like to rent a room.
NPC: You can only rent one room at a time. Sorry. (This topic would be linked under GREETING as one of the Choices.) In the same Condition box where you set who the NPC who uses this dialog is, add a condition so that if the player has the key, the player response "I'd like to rent a room" (2nd time) is only available to choose if they have the key.

The condition would be:

Condition Function: GetItemCount
Run on: Target
Function Parameters: **your key goes here** (you have to make a new key)
Comparison >= to 1

That should do it.

EDIT: One other thing. If you're ONLY trying to make sure the player don't keep asking to buy a room, just check the "Say Once" flag for that dialog topic and it won't be available again.

thanks worked like a charm! but i used just < as comparison so that the npc only rents you room if you have 0 of that item and the rent room disappeared then without using choices. but you totally saved my day thank you!