Evil twin attack on Wi-Fi network has been a challenging security problem and several solutions have been proposed to this problem. In general, evil twin attack aims to exfiltrate data, like Wi-Fi and service credentials, from the client devices and considered as a serious threat at MAC layer. IoT devices with its companion apps provides different pairing methods for provisioning. The "SmartConfig Mode", the one proposed by Texas Instrument (TI) and the "Access Point pairing mode (AP mode)" are the most common pairing modes provided by the application developer and vendor of the IoT devices. Especially, AP mode use Wi-Fi connectivity to setup IoT devices where a device activates an access point to which the mobile device running the corresponding mobile application is required to connect. In this paper, we have used evil twin attack as a weapon to test the security posture of IoT devices that use Wi-Fi network to set them up. We have designed, implemented and applied a system, called iTieProbe, that can be used in ethical hacking for discovering certain vulnerabilities during such setup. AP mode successfully completes when the mobile device is able to communicate with the IoT device via a home router over a Wi-Fi network. Our proposed system, iTieProbe, is capable of discovering several serious vulnerabilities in the commercial IoT devices that use AP mode or similar approach. We evaluated iTieProbe's efficacy on 9 IoT devices, like IoT cameras, smart plugs, Echo Dot and smart bulbs, and discovered that several of these IoT devices have certain serious threats, like leaking Wi-Fi credential of home router and creating fake IoT device, during the setup of the IoT devices.