Tell your brother there is nothing wrong with purchasing a brand new mower from the so called "big box store".
If your brother purchase's it from the so called "big box store" and after a couple days is unhappy with it, then yes he can return it to the so called "big box store" within the allowed time frame, number of days of course.
If your brother purchase's it from the so called "big box store" and is happy with it then great!
Definitely nothing wrong with purchasing from the so called "big box store".
I purchased my Hustler Raptor Flip Up back in 2016 from Lowe's, brand new. No regrets!
Lowe's gave me the best deal and beat out all the other Hustler dealership offer's that I previously had been to when I first was looking to buy.
Lowe's gave me a generous retired military discount and even delivered it to my home free of charge.
No Hustler dealership never offered any type of discount.....not even free delivery. Every time I would inquire about the discount or free delivery they quickly would say....."No Discount".... on anything!
If I purchased it I had to either take it myself or pay to have it delivered.
If your brother decides to buy a Hustler mower brand new and decides to keep it (regardless if purchased from a big box store or Hustler dealer) the first thing he need's to do is register his specific model, etc. with the Hustler website (don't rely on the dealer to do this for him). Hustler gives the customer 10 days from date of purchase to register the new mower. Tell him to make sure to read the Hustler's Owners Manual (that comes with his mower) first and foremost (many individuals don't) and become familiar with Hustler's warranty coverage.
If in the future your brother has a problem(s) with his new Hustler mower (and still falls under warranty) then he should do two things:
1.) Contact Hustler and report the problem
2.) Take it to an authorized Hustler Service dealership (not to the big box store).
If out of warranty then he can take it to any Hustler Service dealership or to any other service place that he feels comfortable with (or fix it himself?).
I've even had my mower taken to a Hustler Service Dealership for warranty service maintenance and have never had a problem.
Good Luck to your brother on his choice.