Instore credit, gift certificates or if a coupon discount brings something below the minimum it will go through but as for putting an item in your cart that is under the minimum 3.50 and use no instore credit, gift certificate or a coupon that makes the total go below the 3.50 it won't allow you to checkout. It is possible to have an order total of LESS than 3.50 by the methods I just listed but as I stated the minimum has always been in place in all the years I've been here, it was 5.00 then when prime started it was changed to 3.50 and as I believe I also stated somewhere there may have been special promotions years ago that it was lifted for a small period of time but other than that it's always been in place.