Yes all settings are correct, and the network type and encryption are compatible.
From another PC I can see the tablet's ip address and MAC address on the router's set-up page. The tablet's settings show Wi-Fi connected and give the Wi-Fi speed and signal strength. From this I infer that the tablet is connected to my Wi-Fi network.
Having done some reading online, it seems that these particular tablets do have certain Wi-Fi issues, but I can't find any solutions posted.
I think I shall tell the owner to take the thing back to the shop and ask for a replacement.
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