"저의 집을 사세요!"
Translation:Buy my house!
Because of the direct object particle, -을, in 집을. It means that 집 'house' is the direct object of the verb, so 사세요 has to mean 'buy' instead of 'live'. If the locative particle -에 were used, it would mean "Live in my house."
It could mean buy in my house if they had used 에 but probably not in this case
No, when there is an action taking place somewhere, the postposition ~에서 is used. ~에 is used for static location or direction (or telling time).
Are there multiple cases of a verb's interpretation depending on particles that imply a different meaning or restriction?
So is 세요 that is added after the verb gives the permative meaning? Like as an order?
You mean imperative. ~세요 can serve multiple purposes, depending on context and inflection; it's the polite present tense declarative (for statements), interrogative (for questions), imperative (for commands) and suggestive (for suggestions) ending.