They let you order things that they either can't get or don't have in stock. If one item is out of stock, your order just doesn't come or is cancelled. My order made nearly a week ago for a seriously ill cat still hasn't arrived. I've spoken to them over a dozen times, from first line agents, supervisors & up to quite senior management. The senior manager 100% promised our order would be here today, we've waited all day - NOTHING. The reason.... in the meantime, another item has gone ex-stock, so they've stopped the complete order without a phone call, text or email. If your item is in stock, no problem, but if you've made a complicated order watch out, their systems can't cope with it.