He only saved $300 for a 2012 with a HDD. Longevity cannot be questioned; look at the asking price for a 2012 windows laptop versus it's 2017 variant for comparison.
He took an L financially because of the longevity. He'll spend more than $300 on a decent SSD + ram easily.
He should need no more than $150 to upgrade to decent SSD + 8GB (which is all you need for average use. Battery can also be replaced for around $50 non-OEM and a little more OEM. The L here would be if he purchased the 2012 MacBook Pro from a retail store, as they have jacked up the prices of these models due to their compatibility. I found one for my spouse for $400 in like new condition on ebay. Popped at SSD + 8GB RAM for a little under $150 and was done with it.
Also, the 2013 Retina model that was $300 more was likely the 4GB/128GB model, which is absolutely not a good ideal in 2017 (it wasn't in 2013 either),