The article points out some really important downsides of tariffs for any business but particularly small businesses:

Unlike sales taxes or income taxes they are paid up front, before the sale.

If they don't make a sale due to tariffs they still have to pay them and end up with unprofitable inventory.

Tariffs can change at any time, and order/shipping times are long, so they are very difficult to plan for. Products may have been ordered months before tariffs but end up liable.