Quality score is that closely guarded secret of Google, but it comes down to a lot of factors that we could apply to a real world social situation. Google looks at technical things like load speed, site architecture, intellectual things like number of inbound links and the quality of the pages linking, and on-page factors like content, its quality, and how fresh or original it is.
If you think of two people at a party sizing each other up, they can look at many of the same things... What does he look like? Who at the party thinks he's good looking? Is he smart? Who thinks he's smart-- Do smart people think he's smart? Is she rich? Is she well connected? Does she say intelligent, well researched or original things or spout the latest thing she saw on Facebook? We can connect a lot of dots between attraction and Quality Score.
So what about Keyword Bid? Well-- if you have a lower quality score, you can increase your page rank by increasing your Bid. I see this as the equivalent of Breast Augmentation Surgery or a Fancy Mid-life-crisis Sports Cars. (Trying to be non-gender specific here). If quality is low, you must make up for it with money to have the same effect. There certainly is a point (as my friend from Google will gladly point out) that no amount of money will make the page rank higher. In the math world, this is multiplying by ZERO. If quality is ZERO, then no amount of money can make the product something other than Zero. Zero x $1,000,000 is still Zero... :(
So, like any society, those with lots of money (or more than average) seem to be able to attract beutiful partners, even if they are of lower average quality. And-- thankfully, those of high quality character, intelligence, looks, personality, etc manage to do o.k. as well. It's the people with no money AND who are 'low quality' (according to the vanity measures just outlined) that seem to have the hardest problem finding love.
Broke, Not intelligent, Not great looking?? You'll find someone, but they're likely to be of similar 'Page Rank'. Don't worry though, you likely won't notice. It's natural selection, some would say.