[UPDATE!] infinite money in pokemon alpha sapphire/omega ruby

if you are having trouble getting money in the recent pokemon games [omega ruby and alpha sapphire] there is a simple way to get spare cash. to do this you must have 1. beaten both Roxanne [level 15 max. I suggest using shroomish, mudkip, lotad, wingull, or combusken if you battle with torchic like crazy] and brawly [bumped down to level 16 max. I suggest tailow, wingull, torchic/combusken w/ flying type move.]  [the gym leaders]. and 2. gotten the tm "thief" from the team aqua grunt in the museum in slateport. after that you teach thief to any high level pokemon that can learn it, being sure that it has no held items. then simply use the search feature in the dexnav that lets you look for wild pokemon by clicking their icon and searching near tall grass. [you can only do this if you have caught the pokemon.] when the pokemon pops out you need to slowly move towards it. get close enough and the search feature should tell you the pokemons level, first move [generally an egg move], ability [typically use this to find secret abilities like a wurmple with run away.], and whether the pokemon has a hold item [and thusly what that item is]. find and battle pokemon with items [any held item will do], battle them, then use "thief" to steal the pokemons item.

repeating this method can allow you to get near infinite numbers of items from various wild pokemon quite early in the game. [which helps with buying items you REALLY want.] this method is also a bit more efficient than using pokemon with the "pickup" ability [as every battle wont guarantee an item. 10% means 1 battle out of every 10 gets an item.]

for this method to be less frustrating its best you walk into the pokemon that your dexnav search expunges from the tall grass as missing them [via moving too fast, annoying npc's moving I your way while trying to walk, running into normal wild pokemon while walking towards the magic spot of majestic black mystery, or other methods of screwing up.] typically causes the dexnav search function to turn around and kick you in the grapes.

just use thief on pokemon that the dexnav lists holding various items. then sell those items. [I have so much stolen honey from surskits I could make a cleptomaniac bee shit its draws.]

[UPDATE!]

ok so another way for infinite money that is a bit les complicated:
past mauville city is four boulders you can use rock smash on. [located above the winstrate family house]. simply smash the boulders using rock smash [try zigzagoon as it can learn cut, rock smash, surf, and its pickup ability helps you get more items in the case you run into geodude]. just smash the four boulders, grab whatever comes out, then go into the winstrate house, leave, and re-smash the four boulders.
I got tons of pearls, big pearls, stardust, ethers, max ethers, soft sand, hard stones, and other items that I sold to get ass loads of money.
this method is simpler in gathering money quickly.

[you can also equip a luck incense/amulet coin and rebattle the trainers using the dexnav. be warned that if you don't have at least two pokemon above level 22 or so you may get your ass kicked in the effort to spam trainers.]

[also using the lunch room in new mauville with the above items also gets you money quick, but only if you manage to defeat the trainers in one hit. finish the battles In the turns specified by the food you order and you get a free nugget.]