There can be issues if you're not prepared for a job in the Warhammer game system. The entire goal is to roll low, to start. Your starting max skill is at 45, for example. That means if you want to hit someone with a stick, you have a 45% chance of hitting base. It's the same odds as someone in D&D with a to hit bonus of +9 smacking someone with AC 20. Now you factor in modifiers;
45 Base from your Weapon Skill.
Weapon quality can give you another +5 to +10.
Aiming (a half action) gives you another +10.
A custom grip is another +5.
If you Charge, it's a +20.
If you have buddies nearby/flanking, each buddy is another +10.
So, assuming you are prepped and go in with a buddy, that goes up to a 100 to hit your man-sized target (this doesn't include modifiers for target size, negatives for visibility or something, etc). Given 100 is basically your natural 1, that means you have a 99% chance to hit. Your smart Bushi should meet a good number of those criteria, if not all of them (and if they're not smart, you've still got a decent chance of hitting!). In the Dark Heresy game I'm running, the sniper when he has no time to prepare has a... +47 to hit on his base of 55? He literally can't miss without rolling a 100, and the dice gods bless him anyways. He's capped out the bonus on rolls you can get a time or two now (which is a +60 on top of the skill). That said, guns have a different criteria for bonuses.
Skill challenges are a shady area, partly because some need equipment, and some don't. If you try Medicine tests without tools or equipment, you take some heavy penalties, but with them you get bonuses. Knowledge checks have penalties based on the depth of the knowledge, so a reference can help, but your basic lore rolls are easy enough. It's hard to stealth in the middle of a sunlit street, but moving in the dark, especially if you go around with some camouflage to blend in even more, works great. Blatantly lying or trying to lie to someone who has no reason to believe you is more difficult unless you can provide evidence to back it up. It's really a matter of doing things properly. If you're going to climb something, bring some rope and a hook. If you're trying to live in the woods for a bit, bring a survival kit. If you're going to pickpocket someone, make sure there's a distraction.
I'm glad to have helped, by the way.