It seems like a simple and low-value task to haul away a bunch of junk but anyone that has tried it knows just how difficult it really is.  Most of the time the task of having the pile removed can be more of an effort than actually creating the pile.   Being a provider that is dependable, honest, and well-mannered will set you apart in this market.  It may seem trivial but showing up on time, having the right equipment to do the job, and presenting yourself in a professional manner can go a long way.  Being a cut above the rest will also help you charge more and get more repeat business.

The capital investment is really low if you already have a truck.  Maybe you get a few t-shirts or polo-shirts printed so you and your helper look good.

Be careful you do not assume liability for anything hazardous or expensive to dispose of.  In some markets, you may need licensing for remediation and hauling household waste.