Good for you for being concerned about that! Most RV dealers wouldn't care.
If their TV is rated to tow 5000# you should discuss the issue of payload with them. That will be more critical than the tow rating. There are some members here who tow with small diesel SUVs (VW or Mercedes Benz) that are very capable tow vehicles. A Honda Ridgeline truck with a 5000# tow rating will be less capable of heavy payloads.
If its a family with kids I'd be more reluctant to sell it to them than an empty-nester couple but they still might want to take grand kids for a camping trip.
Everybody is going to have a different comfort level when towing an RV. I towed our previous Roo 23SS (5200# loaded) with a Toyota Tacoma TRD rated at 6500# and I wasn't comfortable so I upgraded to a F-150.
Bottom line... If your conscience is telling you it won't be safe for them, don't put yourself in a situation where you lose sleep worrying about whether or not you did the right thing.
2011 Rockwood Signature Ultra Lite 8293SS, 12K Equal-i-zer
2016 Ford F-250 XLT SuperCrew, 6.2L, 4x4, 6'9" bed, 3.73
2010 Rockwood Roo 23SS (2012 - 2014)
2009 Ford F-150 XLT SuperCrew, 5.4L, 4x4, 5'6" bed (2012 - 2016)