FWIW, video editing apps tend to be very core hungry!
MacMini Geekbench scores for Multi-core apps:
2014, 3.0 GHz i7 - 6858
2014, 2.8 GHz, i5 - 6596
Not really much of a difference. However:
2012, 2.3 GHz, i7 (quad core) - 10103
2012, 2.6 GHz, i7 (quad core) - 10867
In terms of performance, you may actually want to
consider the older Mini for video. The only drawback
is the lack of 4K support. Then again, if you are considering
4K, the Mini would be woefully in adequate.
There are many places that sell 2012 Minis that have been tested
and certified and warranted. One place to check out would be
OWC. The are a highly respected vendor of Mac accessories
and sell the entire line of used Macs, all of which come with a
90 day warranty and a 14 day return policy.
https://eshop.macsales.com/shop/Apple-Systems/Used/Mac-mini
I am sure there are others out there just as reputable, but I am
familiar with these guys.