Sometimes, they just try to phish for your contact info. This is were a free Google Voice No. comes in handy. It just forwards calls to your real phone number(s). You can also send callers you don't want automatically to voicemail, or block them completely.
I always include a Google phone no. with my Craiglist(CL) ads. If CL blocks it, just overlay the phone no. on all your photos. My experience has been that serious buyers will want to call or text you. Those with a passing interest tend to email. It's also helpful in avoiding scammers as they don't want to reveal their phone no. which is easier to trace back then email.