I think making sure you don't get hosed on the purchase is probably the most important decision--this can save you hundreds of $$$.
Sure, there are two sides to the transaction -- the "trade-in" (if you do) + the "purchase." I sold my iMac to Experimax locally and they gave me a great price, if you're lucky enough to be near one. Usually Apple & BestBuy are about the same, but BestBuy will hose you if you don't include the power brick while Apple doesn't care. However, sometimes BestBuy will run "apple trade-in" promotions where they give you an extra 10% on top (if you're buying another one, of course).
Either way, found it best to go to big box retailers when they are running sales, especially MicroCenter, but can get good deals at BestBuy especially if price-matching. BestBuy gave me about $70 less for my M1 Pro than Apple would have on trade-in -- BUT they gave me over 28% off my base 14" M3 Max. That was a good deal.
MicroCenter also sells APPLE certified refurbished Macbooks (just look for factory refurbished in the title). They don't always have them, but when they do they are also much, much less than the Apple Refurb store.