I know there are frequently 'minor' differences in machines from the big box stores to the LQS or dealers shopes. It often comes down to prices and are you willing to give up a decorative stitch or 2. I would think it is important to check out all the specs. on any machine you aer looking at. Then make your decision. Sometimes it may or may not be worth spending the extra money.

I've done both. I bought a Juki on Amazon that is all mechanical and I love it. I bought both my Berninas at my local Bernina dealer. I've know her for decades and trust her completely. That means a lot to me.
I've also bought old Singers on Ebay.
I guess it depends on what machine you're buying. (at least for me it does)

When i worked at a vacuum cleaner store i was told the same things. They make same model - yet different - for the big box stores compared to the authorized dealers.

Sewing machines
 

I buy on line from a Dealer....not a quilt shop that sells more fabric than machines. You can always deal on machines at a dealer...they know you can get a better deal on line and no sales tax...negotiate those dollars at you local Dealer. I have had no issues at all buying a specific model from an online dealer. Of course, you don't get free classes...but most of the brand name machines have online tutorials.....an you normally get a DVD and manual.

Every machine will need service at some point. Most shops that offer machine service will not service a machine bought at Wally World. If it is a cheap machine you purchased at Wally World you might consider it a throw away if it needs a repair. You can get it cleaned, but probably not repaired.

I eyed a Pfaff at LQS then it went down in price during Black Friday week so I decided to pull the trigger. Not high end but exactly what I wanted & no crowd to fight either.
Store employee spent about 1.5 hours with me.
It came with a free 1st year cleaning & maintenance which I didn’t realize until I picked it up. ($80 value)
When I come in the store for fabric, etc they recognize me & I feel valued. They’re Mom & Pop so he’s the repair guy.
Chain & Big Box stores won’t do any of the above & my parents always shopped local stores.

Our DIL always has a head of steam for Black Friday bargains & get up in the middle of night to get there but she said she’s done buying some things like small appliances on BF because they don’t last long.

Speaking of “Sales”. It irks me to no end when stores put items in their sale ad & I know it’s every day price.. Our big local grocery chain does this every week - it’s a 10-12 page ad with nice colored pictures but only about 1-2 pages have a real sale price.