Ancova with multiple independent variables and 1 categorical variable


I am new to running Ancova in R. I am trying to see if my categorical variable (time) is significant in my dependent variable (Sales) while holding all other variables in my model constant.

aov(Sales ~ Price+Merch+ACV+Items+Category+Time, data = PintsT)

My question is how are you confident the Pvalues are relevant when holding the other variables constant? Does it automatically assume this using a type 3 analysis?

Also when would you use * instead of + in between the independent variables?

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