Ben:
While generally a private airstrip is better than a soft farm field, a good rule is to never set up a final glide to a private airfield that you have not seen recently - even if just from the air. There may be issues with width (especially in corn country), hay bales, mowing equipment, overgrowth, etc and sometimes it has simply vanished or been planted over. I've never been unwelcomed by a private airstrip owner but I have had some last minute surprises that would have been better to avoid.
ROY