Reading the rules of most books, "obvious error" is not defined. Everyone knows that if a book puts up +3.5 on an NFL game when the market is -3.5, that is an obvious error. In every single dispute I have ever seen with SBR, the market price is a starting point to determine whether there was an obvious error. What if there is no comparable market, like in props? The legendary Henry chewed me out once for voiding wagers once. I screwed up, and a price was set at pick when the fair price was about -500. But, there was no market. Per Henry, "When there is no market, you can't void bets for a bad line".
The market price is the standard for whether there is an obvious error. If you start looking at line movements to determine this, you are suggesting that a weak line put up initially can be voided if there is a big move. There was an NBA game with a 6-point move near the end of last season. Was that bad?
I once wrote for the Pinnacle Pulse about bad lines. Let me quote myself... "A general rule of thumb is that a number is bad if it gives you a 7% EV (expected value) versus the market price." (Pinnacle Pulse #25, incorrectly listed as #24 here:
http://www.bettorsworld.com/pinnacle-pulse/24.htm )