Any time I book through such sites, I opt in for their nominal travel insurance (trip assurance, whatever they want to call it) fee- $10 or $15-- covers last minute cancellations for any reason, lost luggage, etc. I think everybody should do this, because even on a $200 ticket or $50 hotel, it’s a nominal fee for peace of mind. If you didn’t. . . well, this is the type of thing trip insurance is for.
Innnnnteresting. I buy probably half of my tickets directly through airlines and the other half through travel depot websites (Orbitz, Kayak, etc.). I’ve never run across this (even the airline bottom line tickets that are “OMG NON REFUNDABLE” usually say they’ll exchange it out in tiny tiny print, from what I’ve seen), but I’ll definitely defer to you here, since you were an agent!