You can do this in illiquid markets, if you fully understand market mechanics.
You need to find markets with no MM's participating where spreads are quite wide.
The SETs platform on the LSE with direct market access is a good example.
There are dozens of illiquid markets with large spreads where the arrival rates of market orders are too slow for market makers to bother with.
If you are prepared to spend all day testing the liquidity at touch of both the bid and the ask by demanding quote at best orders. You will come to learn that sometimes the liquidity at touch is fairly balanced and sometimes there is a significant imbalance.
When you find such and imbalance you can trade it.
When it is difficult to buy, you buy.
When it is difficult to sell, you short.
You should also set up some software to measure the arrival rate of buy market orders (BMO's) and Sell Market Orders (SMO's), as an imbalance of arrival rates has the same effect as an imbalance of liquidity, although arrival rate imbalances are less stable and less predictable than liquidity imbalances.
You can easily find 2 or 3 moves a day of 2 or 3 % each. The only limit is that you will not always get the full $50,000 of you account into these trades.
By definition there is limited liquidity available to take advantage of such opportunites, which is the main reason why the major institutions do not bother with them.
What you are effectively doing here is front running large buyers/sellers who are attempting to allocate large sums of capital into illiquid assets and suffering price impact as a result. That price impact is your return.
As a small time private trader such opportunities are your bread and butter.
NB this method will not work on SPX or AAPL or XOM, those markets are too large and too fast for you to ever get a stable quote at best.
You need slow and illiquid markets.
$500/day? Very easy. You can probably do it with $25-30k.
But there will be times when you run into trouble.
Ignore the dozens of people here who claim only the best in the world can achieve such a return as 1%/day. That's BS.
The smaller you are the greater return you can achieve. But then you don't stay small for long.
More money, more problems.
As you get larger and larger your yield drops and drops as only oppoprtunities with ever greater liquidity are worth your while and competition for such opportunites is extremely fierce.
The problems of money management and price impact are very rarely discussed in public because those who suffer these problems know that giving them air time is an invitation for an army of small time traders to try and steal their liquidity, thus exacerbating the problem.