Well, actually full boils are the preferred method of doing extract with grains, it's just that not many who start out with it, have the capability to do full on boils. And when they do they usually leap to doing All Grain. But there are plenty of extract brewers on here that do it.
And as to LHBS information; Remember to a lot of LHBS'er or employees, it is only a job..not an obsession...so they are not always as necessarily passionate, or zealous learning new things, or trying new techniques, like we are....Some even though they have been in the business forever, may never had progressed in the hobby beyond extract kits...some may rarely brew at all.
So often it is not surprising that we know more or are at least in touch with more info that someone who does it for a living....
This is an ever evolving hobby...Places like this is where you find the most state of the art information/wisdom about brewing, because of the sheer number of us trying new things, hearing new things, and even breaking new ground and contributing to the body of info on the hobby...Look at some of that inventions that came out of here, and then ended up later in BYO articles by our members...
It is podcasts and forums like this where you will find a lot more state of the art, or current views, and even scientific information...I mean if Jamil, John Palmer or Papazian even farts on a podcast, one of us beergeeks are going to start a thread on it within 10 minutes.
So if you are dealing with ab old school LHBS owner/employee...don't back down, and don't let him get to you...
We have threads like this all the time
https://www.homebrewtalk.com/f13/bad-advice-i-got-lbhs-thread-141546/#post1608689
But I caution folks to just blanketly say they get bad advice from their LHBS, when in reality often they simply are getting oldschool advice. Like the long primary/no-secondary ideas. That for us here has been pretty much the cultural shift in brewing, but it is only now catching up in the larger brewing community after BYO, Basic Brewing, Jamil AND John Palmer weighed in on it, but MANY old school types, on here and in homerbewshops are still operating under the 20-30 year old yeast fear that people like papazian wrote from, the "Autolysis" bogeyman, get the beer of the yeast asap philosophy, so for many folks it's like running into a brick wall.
Remember- It is HUMAN nature to scorn that which we don't understand... It even happens on here sometimes, when someone attempt to break new ground, or suggest something different from common wisdom (we still get people who scorn the idea of long primaries, and still believe in autolysis)...but it really is not the norm here.
But not necessarily "out there" in the world of Home brew shops.
In fact if you have one like that, Don't even tell him what you are doing buy your stuff, give him your money, and whistle your way out the door..knowing that what you might be attempting is probably light years ahead of HIS knowlege base.....
And more than likely your beer will end up better than his!!!