Yes, what you're describing there is social problem, not technical. The suggested checkbox would just become one of those "yes, I've read terms and conditions" thing people click through routinely. Unlike in raid finder though, the PF has one benefit, that is the party chat, more awesome now that it's cross world. You can engage the arrivals to conversation befire entering the duty, to gauge how far they are in the progression. If they lie there, they wouldn't have respected the description anyway. If they are honest, you can politely tell them that they may need to start in a party closer to their level.