Buying Mi mobile trick or Any way to buy

Flash sales are not fake, they are one of the ways of attracting customers, it's a marketing tactic.
There are many scripts you can find if you google it, but many of those won't work.
To buy a phone in flash sale use high speed internet and login to the concerned website before the actual time of sales.
Or if you are using any other Mi phone than try the MIUI forum or the MI Community to get your F-code which will help you to buy a phone without any flash sale.
Hope this helps.