After signing up through Unidays with an edu email via this link
This takes an additional $54.02 amount off of the S8+. Thus when you add in the -$200 from the working smartphone, the -$100 from the promotional discount, and then you add an extra $54.02 it turns out to be $470.02 before tax which is better than the $525 from before .
Shown below is an enclosed screenshot of this with the the UniDays discount.
Edit: Based on everyone claiming this is a repost it is not based on the slick deals Rules which states "It's not considered a repost if the information is not part of the OP, FP or Wiki before the new thread is made." In the original post which is this below there is no education discount shown https://slickdeals.net/f/10259068-64gb-samung-galaxy-s8-unlocked-smartphone-425-s8-525-w-any-smartphone-trade-in?src=SiteSearchV2_SearchBarV2Algo1