Home gambling rules
Being a professional gambler has higher reward and higher risk than any other career choice. Being a professional gambler requires 8 hours a day of working on your profession(4 hours a day can be done for an increased dc of +5, but reprisal percentages are increased by 5% for each day you gamble in this fashion). The amount of money you can make per day and per week is listed below in the chart that follows. These values are based on pathfinder settlements base value for wealth. (Daily max bets are based on 10% of item by value availability per settlement size.) The most you can make per day is equal to double your bet money or double the daily max as outlined in the chart below (Whichever is lower). the most you can earn per week in a settlement is based on the weekly max figure provided below. Betting has a chance of upsetting the locals if you are too "Lucky" (Lucky is the term being used though rules for cheating will follow as well). If you earn the most you can during a duration equal to a settlements reprisal rate the gm should roll a reprisal percentile in secret, and if the roll falls below the settlements reprisal chance people will have taken note of your luck and act accordingly. (Local crime boss forces you to play a rival of his with threat of death if you fail, locals run you out of town for cheating, people refuse to play you in that town. If running fame and infamy systems making a character infamous for gambling is a good way to go.)
Examples of reprisal rates being met.
if a person wins double the daily bet 3 consecutive days in a small town. (These days do not need to be in a row, just with no days of losses in between)
If a person wins the weekly maxin a large city
town size daily bet weekly max dc reprisal % reprisal rate Perception
thorpe 5 50 13 5% daily 12
hamlet 20 200 15 12% daily 14
village 50 500 18 18% daily 16
small town 100 1000 20 25% every 3 days 18
large town 200 2000 23 30% every 3 days 20
small city 400 4000 25 40% every 3 days 22
large city 800 8000 28 55% weekly 24
metropolis 1600 16000 30 75% weekly 26
Gambling as a profession requires daily rolls. The DC listed is the dc required to make back 1/2 of your bet as extra. AKA bet 4 earn 2 end with 6. Beating the dc by 5 or more allows you to earn double your daily bet. Not making the dc means you break even, missing the dc by 5 or more means you have lost your bet entirely.
Cheating, using magic, and having an advantage.
Cheating is a great way to make it a little easier to earn money but has a higher chance of you getting caught. To cheat you roll a sleight of hand check against the settlement size perception check. If your check succeeds you lower the dc of the gambling roll by 2, plus 2 for each 5 that you beat the dc by. Failing to make a cheating check involves an immediate reprisal role from the gm with an additional 25% chance of reprisal. On any day you fail your cheating check you lose all money that you bet that day.
Magic rules are very similar to cheating with some minor adjustments. A: you use spellcraft instead of sleight of hand to make your roles. B: up to gm discretion depending on how common magic is in a city extra modifiers may apply.
No magic: -10 to settlement perception
Low Magic: -5
normal magic: 0
common magic: +5
high magic: +10
(high magic refers to a city that likely has people detecting magic around gambling houses and taverns where cards and dice are played.)
Having an Advantage:
There are many situations that could further change the dc of gambling within a settlement and we will refer to these as advantages. The number listed next to the advantage below is a number that the DC is reduced or increased by for settlement advantages. Skills listed only apply if you have five or more ranks, at 10 ranks the bonus is doubled. Advantage bonuses and penalties do stack.
Advantage Adjustment Game
Bluff -2 Cards
Sleight -2 Dice
Diplomacy -1 Cards
Appraise -2 Cards
Intimidate -1 Cards
Stealth -1 Dice
Sense Motive -1 Cards
*Perception -2 Cards / Dice
Glibness -5 Cards
Lie Detection -5 Cards
Aura Detection -5 Cards
Detect Thoughts -10 Cards
*This bonus only applies in areas where cheating is common
Lawful +2 Cards
Good +1 Cards
Evil +2 Cards / Dice
Militaristic +4 Cards
Organised Crime +5 Cards / Dice
Too easy to make too much money to quickly. The rules are also complicated, which will make them difficult to run at the table. Which means your fellow players will be sitting there doing nothing while you live out your gambling fantasy.
Just stick with the already existing profession rules to make money (which wont make it at this overwhelming rate). I'm sorry, but your house rule suggestion is just too good.
It takes a day of gambling down to a couple of rolls, or single if no cheating or magic is involved, and gm's choosing to utilize it will probably already know what the modifiers for their towns and cities are so it really shouldn't be difficult to run at the table at all. As for making money quickly, yes it has that potential, and also the potential to lose it quickly, or open up interesting role playing challenges / encounters from reprisals. It isn't intended to work as the other profession rules or it wouldn't have been posted.
Check out the grand OGL wiki's entry for quintessential Rogue: Profession(gambler) or profession(thief) let you use basic profession rules for low risk gambling or thievery. The book did include a more complicated system for higher risk stuff too iirc.
The Game Mastery Guide has a section on adjudicating gambling and games of chance