Can a student with 50.7% in 12th get into IIFT Delhi after getting 71% in undergraduation, and get a good placement?

Yes, with this score IIFT Delhi will accept you. But it also depends on your undergraduate performance, IIFT entrance exam scores, and qualifications and experience. 

IIFT is well-connected to worldwide trade and commercial companies for placements. However, a student's placement possibilities rely on their qualifications, experience, and job search efforts. IIFT's admittance process is quite competitive. 

Thus, you should prepare effectively for the entrance exam, have a great résumé and/or work experience, and network with alumni and other field specialists to increase your chances of admission.