So short answer to the original post, No single action or ability sells someone on someone else. And i would challenge that friend of yours to prove it to you if shes so sure it works.
As others have stated maybe the wow factor of "she can fit her whole fist in her mouth" or "she can swallow anything" sounds interesting but that's not what I am going to be basing my consideration on. The strongest suits i see in any potentials whether kink or vanilla is honesty, open mindedness, and one who has thoughts of her own and knows when to speak up or say no.
Now on to the most recent comments:
1. "they tell me I have a wonderful personality, tell me I'm cute, tell me they can't understand why I haven't been snatched up yet and then, without seeing a picture of me, say that they can't date someone my size when compatibility has already been established" These guys are shallow assholes..... not necessarily all of them (everyone is entitled to their preferences.) but if they can make a real connection and fade the moment an undesired body style shows up then they really weren't a good match in the first place and consider yourself lucky they bailed.
Ways to avoid this.......You can list in profiles, ads, etc that you're plus size. Get the filter in right away and hopefully prevent the shallow body assholes from even attempting to communicate.You can also mention it during first convo so that youre sure they are aware of your body type and can decide for themselves to continue or not. Body style has never affected my mind on a sub as a person. I want that emotional mental connection the physical/body is a minimal attribute. There is always someone who will like you 100% all of you the way you are. look for those type people.
2. "I've also heard from this same person that a D-type doesn't want someone untrained (like myself that has fragmented training). Most want someone who is familiar with positions, with rules, with protocols, with household maintenence, with basic respect and etiquette"
This one person does not speak for all doms. If that's his view, great, move on and act as if he never happened. You do you. Be the person you are. Trying to live a lie will only blow up later and make things harder. The kink community is not full of doms expecting every sub be all pro and many years experienced. I have taken on subs in all levels of exp. From brand new day one explorers to ones with 20+ years in high protocol dynamics. Each one was great in its own unique ways.
Also to touch on the whole etiquette part. No one you speak to needs addressed by title during casual convo. They have not proved to you that they even deserve that type of addressing. Good doms know titles are earned through discussion, connection, and trust between both involved. Same as they shouldnt be calling you slave slut babygirl etc. These are personal pet names/ titles reserved for the one you choose.
As far as the lacking of exp on your end, use caution with how you interact with "doms"
lots of guys are here for an easy fap session so be cautious here are some red flags to clue you in:
-demanding you submit to them
-requesting or demanding pics
-automatically assuming you're under their ownership and treating you as such
-requesting personal info
-those not willing to put time in to getting to know you
-the world famous "youre not a real sub if you dont do this"( insert action).... usually comes when you call a guy on his bullshit and he gets butthurt and wants to lash out at you.
lots are just seeking a naive girl they hope to scoop up use for easy play and discard.
hope this helped some and didnt end up a huge word wall.
TL;DR you do you and be yourself. those that cant accept it, fuck them theyre not worth your time anyways.