Rumors on the dungeon.

 For rumors about a dungeon that the DM gives to the players before they go: if they could be a lie. 

Then I'm inclined to disregard them all. I'd rather not indulge any of them if one could be a lie. 

This is an overly pessimist view. 

How do you do rumors and what are your thoughts about them and what have you learned in using them? 

Do you have a philosophy about them? 30% true, 50% half true, 20% lies? 

What's the design point of rumors? to wet the players appetite? To give them clues of what they'll be facing? A clue on how to beat them? 

If they can be lies, then is that to intentionally misdirect them? 

What if the rumors are only true and half truths? 

I don't have answers for this. Rumors certainly aren't needed but they could be a hook for why the players are going to this dungeon. Maybe that's reason enough?

Something to experiment with.... 

Dungeon idea

 Take or make a generic dungeon. Reuse one you've already done and reskin it. 

THEN 

add 4 other adventuring parties exploring it.

The 1 in a million chance. Not only is then another party there's 4! 

roll for their dispositions. Hostile to friendly. Maybe one attacks, one talks, one suggests teaming up!? etc

Have they cleared a room or two? Roll to see if they already got the treasure of some of it?

If you want to add complexity roll to see how they're exploring the dungeon as the players do. 

They could meet up after the initial meet and one or some of them were killed.

They could interact with each other. The players meet both groups and later in the delve find that one group killed the other! Your players come across a room with their bodies stabbed and looted! 

Have a big enough dungeon for this but it can have more than normal empty rooms and increase the chance of meeting the other parties. 

You can have fun and plan things out. Give the different parties themes, flavor. etc 

but this can also be used with minimum prep of rolling to generate them and see what happens!