If you are comparing 2 exact same model numbers, shouldn't matter where you buy them. Big Box stores are DESPERATE for more contractor business, so they are constantly pushing their vendors for high qualitity and lower prices. IMO, most of the "lower qualitity at big box stores" stories are just rumors put out there to discredit Depot's and Lowes since they have deeply wounded the local supply houses
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Those who can't criticize on the internet
I'm with Mr. Chips on the big box stores. No manufacturer is going to change the spec on a particular model number just for a big box store customer. That would make tracking warranty claims a nightmare and give all tools with that model number a bad reputation and it is just not a practice you will find in manufacturing. The case or packaging may be different but the tool will be the same.