If you are new and wanna get some easy cash then fear not this guide is for you.
You're gonna wanna have some semi-decent battle stats and weapons for this. They don't have to be perfect just good enough.
Step 1. Click on hall of fame
Step 2. Choose either net-worth or battle stats
Step 3. Spam the "Page Down" button like crazy or just click on "Your Rank" and browse a bit.
Step 4. Chose a low level person with a generally high paying job.
Step 5. Check to see how long the person you chose has been offline for. For me if they've been offline for 130 ish days or more they're good to hit.
Step 6. Attack them and choose to mug them. You don't want to hospitalize them as that won't give you money.
Step 7. Repeat steps 1-6 for as long as you want.