Accuracy is an important measures of quota quality, measured in standard deviation for the statistically trained, or just % of people within a reasonable band around quota (e.g. +/- 20%).
Another important measure is the shape of the distribution – is it a normal-type curve balanced around 100%, or is there a systematic skew to it? Bi-modal distributions may indicate quota setting issues for a particular category of sales person (new hires, small quotas, etc.). A typical dysfunctional quota distribution is left-skewed with a long right tail indicative of most people under-performing vs. quota offset by a few over-performing outliers, a very expensive way to deliver compensation in a plan with any meaningful acceleration over quota.
Credibility and sales force motivation
Motivation and sales force credibility are most likely only measurable via an opinion survey or poll of the sales team. If sales people understand how their quotas are set, and believe they are generally achievable and equally challenging across the sales team, they will be motivating and help create maximum sales productivity and predictability. If any of these sales force perceptions is unfavorable, it will tend to undermine the value of the quotas to the organization.