John,
"Land Mobile" radio dealers are the folks who sell commecial radios for trucks/taxis/fire departments/police etc - they also sell the fixed side of the system, but in general, they are selling radios meant for 2 way communications on land, where at least one side is "Mobile"

BTW to give you an idea of the difference between even ham gear (which is built better than most GMRS units) and commercial gear - I'm the Radio Mile Post captain at Mile 14 on the NYC Marathon - that spot is what we refer to as "intermod alley" - you go down there with most radios, and your going to hear all sorts of horrible noise on your radio - mostly pagers - you will hear them on almost ANY UHF radio you bring down there - EXCEPT commercial LM radios - they stay silent, and when you are listening to someone talking to you, you don't get the constant screech of the pager transmissions

There IS a problem with commercial LM radios however - depending on what you want, they can cost more money than you probably want to spend (like $1700!! EACH) - then again, they might have a used one hanging around for a < $100. Almost any LMR (Land Moible Radio) will be more rugged, will definately be repeater capible etc - I saw one dropped more than 100ft off a tower a while back - guy got back to the bottom, picked up the radio, dusted it off, looked at it, and made some test transmissions - worked fine - hung it back on his belt, kept going. I carry the same model - I think I paid $75 for mine, and another $75 for second battery - often the used radios are cheaper than a brand new replacement battery

To sum it up - a commercial LMR is meant to be carried, all day, every day, and just WORK - think anout what your local police department carries - that is LMR