We have personal experience shopping software at a varity of retailers and we know the ones we trust and where we've had a great experience. These are the places we will always recommend first.
For us, on Black Friday there are a small handful of places that we would point your towards and it's a mix of software developers and retailers.
Developers we trust include Waves, IK Multimedia and Native Instruments. They all run great sales and we know they're above board. Buying software from them is a breeze and they all offer fantastic customer service.
Special shout out to Plugin Boutique who sell plugins from hundreds of fantastic brands.
Specialist online music retailers have become better on the software front, too. Where you used to only be able to buy physical copies of DAWs, it's now easy to access direct digital downloads at places like Sweetwater, Guitar Center and Thomann of all your favourite plugin brands. And the best thing is that, because software is a download rather than a physical product that needs shipping, you can go for the seller that has the best price!