I buy from PBMG also - PBMG is the parent company of Autopia/Autogeek.
They usually have these 25% off sales a couple or more times a month.
When they run sales like this, yes it can be cheaper to buy from them, but otherwise Amazon is usually cheaper. For example,
https://www.amazon.com/Sonax-230500-.../dp/B00BDOCWMQ
on Amazon it is regularly $75.67. Over $14 less than on the PBMG sister sites. Amazon prime does free shipping though. With this product on PBMG if this is all you are buying your order is under $75 and you either pay for shipping or need to buy something else so potentially with shipping this might be about the same price even with the 25% off.
I do appreciate their youtube videos, forums, etc., but just buying from their site blindly will unfortunately lead to paying a pretty significant markup.