In fact they tend to have opposite signs - consider a 2x2 matrix as a simple example. More elaborate explanations are speculative and unnecessary. This point has high leverage so we should check if it's influential in a given model and perhaps remove it if necessary. Pick the model with age, education, income and price - it has the lowest Cp statistic and is below the line indicating a good fit. The transform of the response differs in the two models, so the usual F-test cannot be done.
Some wraps are significantly different from others.
Only plastic wrap and mixed gas are not significantly different. Post-data so use Scheffe. Zero isn't in the interval so there is a significant difference. Latin square - used because there are two blocking variables equal in no. of levels to the treatment factor. LS is used for efficiency.