In B/X and I believe most OSR games these days the primary source of experience points for PCs is treasure which they bring back from their adventures. If you go with the rules as written the XP gained frok overcoming enemies is tiny to the point of being marginal if you want to have even a modest pace of character advancement in a campaign.
I quite like this approach as it makes lethal combat a means to an end instead of being the end in itself. And only one means among many others. But while giving one XP for every gold piece found in a dungeon and brought back to town works well enough for a game about treasure hunters it does have it’s limitations in pretty much any other scenario. I think mines are a great environment for a dugeon crawl, but how much treasure can you hide down there in an at least somewhat plausible way? Or take adventures in which all the opponents are wild animals or spirits with no use for treasure. Simply putting big pots of gold in random places is neither believable, nor fun.
A simple workaround for this are bounties and rewards. An owlbear with 1,000 gold coins in its cave would be silly. But an owlbear whose head is worth 1,000 gold coins when delivered to the village elders really doesn’t stretch plausibility in any way. (Aside from gold being apparently worth almost nothing in most fantasy games.) Yes, a trophy is not exactly a treasure. But there is plenty of precedent of valuable tapestries and paintings whose only worth is that someone in town will give the party a bag of coins for them, and they have always been regarded as treasure that counts towards calculating XP. Treating reward money for things done in a dungeon as treasures taken from the dungeon is a perfectly valid thing to do.
Another nice trait I like about NPCs announcing rewards for certain things is that it’s more noncommittal than having an NPC hiring the party for a quest. When you send the players on a quest it brings with it the expectation that there’s a planned plot that the players are meant to play out and I think I’ve never seen players deciding to just not complete a quest unless they were obviously set up by an evil NPC. A notice of reward is much more open ended and more of an optional objective that can be done when doing stuff in the dungeon. If there’s plenty of other stuff to do and grab, players are more likely to think twice about asking a dragon for his head or taking a gem that keeps an underground garden alive. Decisions are always the most interesting when there is no obviously better option to pick.