From so many ways to identify whether a website is using Odoo or not, I have a special technique. It is very easy and not require any technical experience. Just open up your browser and add /jsonrpc to a URL without any parameter. For example: A default odoo installation will response with recognizable error message:

<function RPC.jsonrpc at 0x7f51dfc01268>, /jsonrpc: Function declared as capable of handling request of type 'json' but called with a request of type 'http'

Identify Odoo with /jsonrpd

If the website is using Odoo, it will return a Bad Request response. Otherwise, it will return a usual 404 error page.