Pretty poor unless you can see it, and take it out of the shop.
Washing machine to be delivered - 'expert' arrives, to install it, has a glancing look at the pipes and mutters something about 'seized' and 'needs a plumber'. I arrived home, fitted the machine in about 20 minutes. I'm not a plumber, it turns out, just not an 'expert' in the Currys sense of the word.
They've offered to refund me the money for installation, and I've found a company that will pay me to take the washing machine, so I'm better off - apart from spending a week with a broken washing machine (the old one) in the kitchen. For big and important purchases that need to be delivered, you're probably better going somewhere were customer service is important to the company name (ie, John Lewis).
Fortunately, the new washing machine is warrantied for 5 years through the manufacturer, so I needn't deal with Currys again.
I've always defended Currys against bad reviews, but I see the reason now!