I for one am very concerned that someone may be able to spoof a device on my WLAN and listen to plain text packets or spoof packets of a device. Do you know how

I for one am very concerned that someone may be able to spoof a device on my WLAN and listen to plain text packets or spoof packets of a device. Do you know how many users would click proceed if they got a certificate mismatch warning not even knowing what it means?