how can i buy and sell btc or other products in bitcointalk forum..
It's very simple there are different market places for your product, if your product is goods then you can post here:
https://bitcointalk.org/index.php?board=51.0 and there are child boards for it. Digital goods, collectibles and computer hardware.
For services go here:
https://bitcointalk.org/index.php?board=52.0 and how can i use escrew here for buy and sell...
Just contact them, the escrow of your choice. Give them a message.
who is best escrew services and how much fees for gud and honest escrew..
For me, I suggest SebastianJU and Dabs.