I don't feel that the amount of feedback an individual has on the site has any bearing whatsoever on the quality of the trade.
I don't think the character of trader can be quantified by their refs. Perhaps it's just that a trader is more inclined to show their true nature when they have a large number of refs. As a new trader, you might be willing to invest more time, be more polite, or even show a tougher skin as a defense. As an established trader who has a large number of refs, you might be more inclined to lean on those refs and less inclined to use a facade. If your innate character is one that lacks empathy or is of arrogance, it could be more evident in your trades. If your innate character is one of empathy and humbleness, perhaps you are even more likely to present a positive trade experience for others.
A second issue is attention to detail. Some people are very detail oriented, and some are not. As a new trader, you might not know what to look for, but you are probably more likely to take the time to look and scrutinize things. As an established trader, it could become routine. You might stop looking so carefully at the things you send out, or when you said you would send them. You might start thinking to yourself as above the rules or that you should be warranted more leeway or that you can get away with more things because you have more refs.
An important note is that I hypothesis that these behaviours are less apparent to ourselves than others. We might not have intentionally meant to sent a card late or sent a card that was actually played when we had it marked as NM. However, we might be more inclined to think we are less fallible. "That person has a fourth of the refs than I do, certainly I could not have been wrong. They must be trying to cheat me."
These are only thoughts based on anecdotal experiences I have had. Between motl and deckbox combined I have a little over 90 refs. In all those trades, I've only had 3 genuinely bad experiences (2 motl, 1 deckbox) that I can recall. All three of those were with traders that had a considerable amount of refs (over 100). In two of those cases, they misrepresented their card condition and tried to pass the blame onto me when I questioned it.
One other small note, people sometimes seem to slide card grading tolerances based upon the value of the card. A $1 rare they are happy to say is SP, but a $35 card is NM unless it's MP or lower. I know 10-30% off the card value is a lot more meaningful on a $100 card, but if a card is not NM, it's not NM.
Thanks for all the replies!