Generally, IMO - Cheap prices + good reputation = fast-moving inventory = fresh stock
Problem is, it's difficult to know. You would have to contact the perfume manufacturer and try to get them to help you identify the bottle/juice production date from the lot/ID codes on the bottle/box (once you receive the perfume). Some manufacturers are more cooperative than others.
Personally, I've always gotten what I believe to be adequately fresh stock from them.
BigDiscount is another discounter I trust to provide fresh stock.
What makes you suspect you might get old stock from Scentmonkey and not Scentiments?