how they generate new bitcoin address for every customers,
what payment gateway or service they used for it?
and how to put options to auto release bitcoins once seller marked trade finished succesfully?
and your recommendations please
Answering your questions one by one:
1. They generate new bitcoin address for every transaction as well as customers by using inbuilt custom script based on core bitconfig
2. Nope, they don't use any payment gateway, rather the transaction is direct, or else they have to give commissions to the exchangers.
3. Auto releasing bitcoins once seller marked trade complete is also accomplished by custom API.
And my recommendation is, study bitcoin core functions minutely, how everything works and then attempt or simply hire a good developer
thank you lot