The obvious weakness in such a deal is that the customer disappears after taking the upfront money. Instead of disappears this could also be "suddenly loses interest in working" or "gets into a car accident and physically cannot work anymore" or any other variation, it doesn't have to be fraudulent or malicious. I think it would be very difficult to find investors who would agree to terms like "10% of income, whatever it is" since it would be so unreliable.

If you change the terms to "give me $X00,000 now, for $XYZ each month over the next 10 years" then you get a regular loan, which is obtainable from a variety of institutions. If you are particularly worried about being disabled or laid off, insurance can cover most of that but those only pay out at the time of any incident actually happening, not upfront.

The standard advice for people who are worried that their current good times might not last is to keep your monthly spending well below your monthly income and build up an emergency fund of at least 6-12 months of living expenses. This will give you enough time for job hunting if you are ever laid off unexpectedly and (more importantly IMO) relieve you from most of the stress of being dependent on your current job to survive. Look up the FIRE/ERE movements online for strategies to get started with this.