To piggyback off what Richard and Heinricht said here:
If you have a character with a mercenary background, depending on how you roll them and where you're rolling, you can discuss that with your prospective plot team. If they don't previously have as many opportunities with rewards up front due to the story of their game, talking to them in advance can help you understand if that's a viable background in the specific lands they're in, or open up opportunities that may encourage more straightforward mercenary work.
With coming in with early XP levels, there's still a lot of potential with that to say in your background that the reason you ended up with the skills and gear you have at the time of game start for you is that you are a mercenary.
For example:
Your character may have moved to the area where the game is occurring because you have heard of it being more risky but also more lucrative (Out of Game translation: the Average Player Level is higher, the level totals are higher, therefore the treasure policy is higher) than taking direct contracts. As a sellsword coming into the area, that change in culture if there is one can be interesting to roleplay out. Instead of getting a mere silver to creatively take on minor monster problems for traveling merchants and minor nobles as something of a soldier of fortune, you hear you could be fighting collaboratively to take down the Evil Power Master and catching gold or better from his minions.
LARP is cooperative, and a smart mercenary would understand the cost and benefit of working with others. Instead of having to keep silver and gold aside to pay directly for healers, the healers in your group will often do it because it makes sense. You're up there hitting things and keeping the threats from getting to the back line where they are, as long as the distribution of resources afterward is equitable, casters and martial classes stay happy.
Taking it as a craftsman skill (for 2.0) or profession (for games playtesting 2.1) will confer benefits worth 1 silver piece per logistics period for each rank at check in. (For Profession, it's either a silver piece or a Crafting Material, which is relevant to production skills.) This is at the rate of 2xp per time you have taken the skill, and adds flavor to your character.
Your play style as a mercenary will be highly dependent on how you want to play as a PC and your own out of game physical capabilities. If you can't hit the broad side of a barn while throwing things, maybe being a sword jock is more your deal. Sword and board is pretty popular. If you're the type to run around all over the place or like to be sneaky beaky and get behind the enemy, scout archetypes might be more your speed.
It brooks mentioning that you will be able to rewrite your character after your first event if what you have made isn't your style.
However: If you aren't sure about your character, you have until the
next event you play as your player character. This could be a month, or it could be the very next day if you go to two mod days in the same weekend. Even if you change the way your character is built, you cannot regain a chance at new starting gear tags, though.
You can also try out different builds in freeplay before going to your first event to see what your mercenary would be capable of here:
https://freeplay.alliancelarp.com/
I'm personally a big proponent of trying to NPC first in your desired chapter. Some camps have free NPCing, others have the NPCs pay a reduced rate to help cover food and camp costs, but you'll be provided costuming and weapons and can talk to your plot team about styles you want to test out. It's a great way to understand the culture of the chapter and can be a big idea generator. I went as an NPC for my whole first year. The experience in understanding fighting styles, the world, and how the rules work from a practical standpoint was a gigantic help.
Regards,
Jack Y.
AGB Plot/Tech Goblin/Baby Rules Marshal