My partner sells small items, mostly custom made or assembled to order, via etsy, ebay and Facebook. She sets aside time every working day to process every order and keep stock availability accurate. She aims to despatch every order by the next post day. I reckon she probably ships more parcels than BD by quite a margin. If she was to screw up, it would hurt her seller ratings badly.
Running an e-shop should make these things easy, but only if you are conscientious about keeping on top.