Which MSCs that do apartment shops are you signed up with? I average 30 minutes on site.
Also, do not be afraid to bargain. I might say that I need 2-3 shops close together to make a trip profitable, or else a significant bonus.
To me it is more unusual for a MSC to limit you to only one shop. Naturally, the limit can only apply to their own shops.
I do not do apartments for less than $50 and get a bonus if there is any distance beyond about 6 miles in this highly congested area.