How magic shops know if the method is new and have never published before?

Well, if the magic shop owner knows magic, then they will know in many cases if the method is old or new. That being said, most methods are based on old principles so not really new.

Most principles/methods of magic have been published somewhere. You would be hard pressed to find a new principle unless it is based on modern technology. Then, it would be recent due to not have been possible before the technology was created.

There you have it!

Thanks for the reply.So basically is knowledge that someone or team have accumulate over the years

Yes, with lots of resources - like Penn & Teller, etc.

One extensive resource is https://www.conjuringarchive.com , which allows you to check for yourself without needing to have the cachet to bump shoulders with the old-timers.

Highly dependent on the owner of the shop. There are some shops that have been around years or with knowledgeable owners, and some shops that the people there only know the tricks that have come out in the last 3 months.