I think it is completely normal for small boutiques to ask this. I sell one of something...as long as the overall quantity of the order is met (I have a quantity minimum and not a dollar minimum). My buyers really like that. It enables them to carry a larger assortment of my items, rather than purchase more of only a few different items. However, that might not fit with certain types of products or businesses. It's kind of a tough one if you have something in your policies and a buyer wants to tweak it ever so slightly. But, this buyer IS willing to meet your dollar amount, right? Even offering to pay more than the minimum required? If you feel you'd like the order, I'd take it. Maybe take another look at your policies to see if this change is something that would work for you on a more permanent basis. Maybe it might be holding some buyers back? I like that the buyer liked your products enough to ask, instead of skipping over you looking for policies from another company that might fit their needs a little better. The jewelry category has the 2nd highest amount of sellers on EW. I don't say that to sway your decision on your policies or disrespect your policies in any way...but, it's competitive out there and if you can work with a buyer and they are willing to pay more than your minimum...and it works for you...it might be worth it.
