It's possible that you've got a fairly small group of low level players, and they need to round out their ranks with a few extra people. Good, competent retainers ask for upfront payment or an advance since they may very well not see any amount of money come from a dungeon delve. Wisely, they'll store this away with their family, ensuring a large amount of funds go to their loved ones even if they kick it (as they usually do; adventurers drop like flies). Since your poor new PCs who can barely afford armor want a numbers advantage, they're SOL hiring these guys.
The sort of person who goes into a known deathtrap that's consumed the last ten people who went in on the off chance of treasure is crazy, or desperate, or has something wrong with them. The sort of person who does this for no upfront payment is possibly all three. Here's twenty of those sorts of people.
Remember, most of these are not known on hiring, unless there's no way for it not to be blatantly obvious.
1 - Non-proficient with all weapons and armor, no class, -4 to Attack Rolls and Armor
2 - Secret Corruption Cultist, allies against party if they fight Demons, Undead, or other fucked up eldritch thing
3 - Greedy, tries to take treasure secretly, will argue loudly for larger share
4 - Lizardman wearing Skinsuit that is beginnning to rot; if isolated with only one other human, will try to kill them and wear their skin.
5 - Very stupid. 2 in 6 chance of doing nothing during dangerous situation.
6 - Cowardly; morale 1, runs away or cowers at first sign of trouble.
7 - Leeroy Jenkins! Morale 12, Will charge into all combat regardless of danger or plans.
8 - Cursed! Automatically fails saves against mind control.
9 - Misplaces items! Any time party needs item they have, there's a 2 in 6 chance they lost it.
10 - Refuses to fight intelligent creatures, even if they would die.
11 - Psychopathic killer! Will kill anything and anyone that isn't a member of the party, with little to no regard for diplomacy.
12 - Thinks they're in charge, will argue with party about course of action, give orders and be annoyed when they aren't listened to, etc.
13 - Crippling Addiction to random substance; has no money and will go into withdrawal at some point during adventure.
14 - Hiding (random) Disease! At the end of the adventure, anyone who came into contact with them or their belonging must save versus Death/Poison or contract their disease.
15 - Corrupted One! 2d6 points of corruption, engenders -2 penalty on reaction rolls to entire party. 2 in 6 chance something else wrong with them, too. (Replace this with mutations or something if you don't use a corruption system)
16 - Fanatically Religious! Will constantly espouse beliefs about their patron deity, and will be hostile to anyone or anything that challenges said beliefs.
17 - Overly curious! If there's a big shiny button or lever or something to interact with, they'll be visibly anxious for 1d3+1 rounds; after this time period, there's a 4 in 6 chance they press the button, pull the lever, or whatever.
18 - Has a price on their head! Group of armed people will accost party, trying to claim price and assume party is accomplices. 2d6 Such armed people will appear (treat as ordinary 1 HD humans) plus one leader (1d6+1 levels, random class).
19 - Geased by a Mage to retrieve a magic item either from the party or from the adventure locale! They don't want to die, so they'll use whatever tactics are most effective to keep said item for themselves.
20 - Actually nothing wrong with them! They just like adventure.
