I'm a huge fan of gas stuff. I detest cords, and every single one of my extension cords is now 3' shorter and has a replacement female end on it BECAUSE OF HAVING OWNED a corded hedge trimmer. I have never had the issues that people complain about gas stuff, and I don't do anything special.
IMO, Stihl makes the cream of the crop. Husqvarna and Red also make high quality stuff.
Anything you buy at box stores will be cheaper-sourced parts, assembled by a third party, and slapped with a sticker. Having said that, it's not entirely a bad thing. Yes, quality will be down. As a former warranty repair guy for HD, the process kinda went like this:
HD and Lowes in the 90's: We need to sell brand name lawn equipment in our stores, and we have the world's largest buying power. Let's pressure the big brand names into making cheaper stuff so we can buy it super low and sell it for less than dealers and still make a profit
Customers in the 90's: This stuff is crap and I will never buy an [insert brand name] again.
Suppliers in the 90's: Umm... duh. you're selling crap and this is bad for our reputation. Good luck with Black and Decker, the only brand left willing to sell to you.
---------------------
Box stores in 2000s: Ok, we'll pay for the good stuff... well, crap, we're not making a profit on this.
Customers in the 90's: This isn't any cheaper than the dealer, and we all remember what happened the last time I bought a [thing] from a box store.
Suppliers in the 90's: We're not selling anything in your store, so why are we going through this headache?
------------------
Today, the chinese stuff is getting so good that all of them are made there. Dealers are holding them to a higher standard and they are producing much better stuff. Now we're back to the 90's scenario, its just that the "second-class" chinese stuff is still pretty darn good. In the past it used to be that you got the good stuff from the dealer which was built in a Scandanavian country or the HF-level crap from HD or Lowes. Now, the difference between the two is very minimal.
If you buy from Amazon, there is a VERY good chance that what you are getting is the same thing you'd be getting from one of those tool liquidation stores in an outlet mall; the box store version that was RTV'd (return to vendor). This could mean that someone bought it and opened it and didn't use it but the packaging is gone/damaged, they found it too difficult to use, they flooded it and it wouldn't start, etc. It could also be brand new, but part of a special black friday shipment where they were assembled by a cheaper bidder and sold in huge quantities. Again, not bad, but just be aware of what you're getting. You have a better chance of getting a good one if the Amazon seller is the brand name of what you're buying. If it isn't, it is a liquidation company that bought refurbed or returned items and replaced parts that showed use (if any)
For instance, THIS one is a Husqvarna trimmer on Amazon sold by Husqvarna. It is likely a brand new trimmer just like from the dealer at a slightly reduced $277 price because Amazon.
THIS one is the same Husqy for $299 on their website.
THIS one is an Amazon refurb unit for $269.
Also, another big factor. They're all more or less getting closer to being the same. Poulan, Husqvarna, Craftsman, and Weed Eater brands are all owned by the same company. Ridgid, Dewalt, Bosch, Porter Cable, Black and Decker, Skil, Ryobi, and Homelite are all now owned by one umbrella under Home Depot. They mix and match certain things, like Homelite's pressure washers are still assembled by Robin, Skil's jigsaws are outsourced from someone else, etc. It's important to note... they are all still assembled separately with some unique parts, but many of the parts are the same thing brand to brand, like this string trimmer part. They're all in each other's beds.
BUT... having said that... for not much more money than big box stores or Amazon, you can get a top of the line Husqy or Stihl. I wouldn't hesitate to buy a heavily used one. They're very high quality.