Crossplatform mobile application needed

I need a professional one to build an application regarding our business. We do software selling and the existing apps need to be like fiverr style with registration and order [login to view URL] should must use xamarin and of course you need to be professional in c#programming. No need cart functionality as that will be used by vendor side via webapps. I allrwady maded the apps wireframe and gui [login to view URL] needed some9ne to makes it real as my requirnment. I could expect a demo before release payment for you. Thanks.