This is a play on words. An "upholstery tack" is a sharp pin used to affix upholstery material to furniture like sofas. However, "tacks" sounds like "tax" meaning an extra fee placed on a bill. Here, an "upholstery tacks" refers both to tacks placed on the sofa and an extra charge for the upholstery.
My sofa was repaired , but I was surprised to find an item on the bill for upholstery tacks .