My accumulated knowledge on gil sellers:
Gil sellers are found at any level. The common misconception of all RMT having a low ranking only applies to the gil sellers who get PLed to a certain level to camp a specific NM or do a specific money making method outside of sky. An example would be the gil sellers who camp Mee Deggi or those who farm tree cuttings in Zi'Tah. They are all rank 1 because their character will never serve monopolization purposes in sky. Gil sellers are only ever rank 1 or 6, only ever being rank 6 for sky access if their character's purpose is sky monopolization.
As for gimped equipment, this only applies to gil sellers who don't have the purpose of raising gil through endgame activities such as camping HNMs. You'll only find scorpion harnesses and god gear on those gil sellers' who's purpose is in endgame. Gil sellers at one time were very unknowledgable about endgame and what it involved. Once they learned through trial and error, they began gettting better and better at endgame activies, particularly camping and defeating HNMs. Now, they invest in decking out their characters in good equipment so the job is easier and more guaranteed FTW.
For the misconception of gil sellers not belonging to a LS, that also only applies to those gil sellers who aren't involved in endgame activies, mostly camping HNMs. You'll only ever find gil sellers wearing LS if they're character's purpose serves in monopolizing endgame activites, mostly camping HNMs. Gil sellers who solo camp NMs like Mee Deggi don't wear LS.
Alot of gil sellers will stay /anon while others don't. Some also have and stay with a gimped SJ (usually because having the SJ leveled won't mesh with their character's gil making purpose), a poor SJ choice, or no SJ at all.
Although some of these things can indicate a gil seller, you cannot judge someone or point the finger at them if they don't respond to you, are /anon, don't have a LS equipped, are a low rank, have a poor SJ, underleveled SJ, no SJ, or have gimped equipment. Their are just too many possibilites out there. Their are many legit players with all of these "gil seller indicators" going for them. When I camp NMs, I may or may not respond to someone, even if they're 1 foot away from my character and I'm moving around. I also stay /anon when I camp NMs. One would have to be the cut down on /tells I get when my <job> is showing in /search. As for my equipment, sometimes it will be gimped when I'm camping because I may be of such a higher level then the NM, I have no risk of getting killed. Sometimes I might want to just throw on a piece of equipment or two from another, lower level job to throw people off when I'm camping. Another reason for having a few pieces of equipment missing from the equipment menu would be for space. Sometimes I'll go out and farm/camp NMs for hours upon hours, filling up my inventory all the while. This way I can make less trips and use my time more to my liking.
So you cannot judge someone and determine whether or not they are a gil seller based on these factors alone. Their usually needs to be other factors known to determine whether or not someone is a gil seller. Factors such as asking them flat out, seeing how they respond, what LS they're wearing if any - their are many ways to detect a gil seller, usually more complicated ways if you want to be absolutely positive they are truly RMT.
All employed gil sellers ARE Chinese while those who aren't employed are pretty much "self employeed" meaning they don't actually work for a company which sells gil, they just raise gil from wherever they play and sell it online for profit.
Some gil sellers work together in game while others don't. Their's several gil selling companies, so I wouldn't think all gil sellers employed out of China know each other. Some gil sellers will respond to you in /tells while other's won't. Alot of times, gil sellers will openly admit they are RMT while others will lie to you. Alot of gil sellers whom you find camping NMs will be AFK while their character is on a program to automatically go for the NM when it pops and claim it. Some are even programmed to defeat the NM and return to their camping position, all while they're AFK.
Most RMT use packet sniffer programs to detect when a NM is about to pop. Most also use 3'rd party programs for warping to NMs as they pop, timer set fast-claiming programs, and other forms of botting.