Why Certify A Common Date Coin

That summarizes it pretty well.

As can be seen on most coin forums, there are a lot of people out there who don't do the homework, see many slabbed coins going for high prices on ebay, and assume any shiny looking coin can be sent in, slabbed, and sold for a high price. They have no concept of what a high grade coin looks like.

I believe a lot of slabbed face value coins can also come from this mistaken mindset as well.

A $5 raw coin can easily become a $1000+ coin IF it grades high enough. A few years ago I purchased a bunch (nearly 60) of a fairly common date Australian coin from a US seller, all Unc and most likely from a couple of broken rolls. Paid about $120 for the lot. Slabbed them a year ago and got 2 in MS67, 22 in MS66, ditto MS65 and a few that scored lower. In MS65 they sold for around $500 (I was outbid on one 18 months ago at $580) and I now own 2/3rds of all the 65, 66 and 67. The submission cost was $15/coin. Not that I'm selling but the slabbing was well worth it. BUT the risk for anybody with the slabbing game and buying highly priced slabs is that it just takes someone to submit a roll of choice coins and the perceived rarity (and value) can be heavily reduced. I'll bet the guy who outbid me probably has some remorse for paying that much when the population tripled six months later.