"These olives are not in the market."
Translation:Hae olivae non sunt in foro.
What is the rule on placement of the verb? It seems that sometimes it comes last and other times not.
There are no rules per se - Latin has an extremely free word order (the default is SOV, not the rule). It depends on what you want to emphasise.
Also, I think it is common practice to have the object after the verb if there is a preposition (e.g in foro). It has been a while since I studied Latin however, so please excuse me if this is erroneous.
It doesn't matter, as you can tell what is the subject or object of the sentence from the endings on the nouns.
As I said in another reply on this post, it is technically correct (it just hasn't been added to the answer pool yet), but I think SVO is more common when the object is paired with a preposition (i.e, in foro).