Gigantic deductions with no income would have them charging you with tax fraud.
Tax fraud would be claiming deductions for expenses that were never incurred. The expense of "rent" was incurred. The expense of "posterboard" was incurred. The expense of "balloons" was incurred. Using your attic for something other than storing items you retail in your online store and garage sale would turn your claim into fraud, but I never suggested you should do anything like that. That you attempted to sell everything in your attic indicates it was not used for personal use. They may not allow you to claim it as a business expense, but they can't argue fraud unless you used it for personal use despite claiming business. So don't do that. Don't use it for personal use when you claim it as a business use.
You can’t get away with deducting your mortgage as a business express from a unprofitable garage sale.
I didn't say deduct your entire mortgage. You can't do that, unless you use the entire home exclusively for business. But you certainly can deduct a part of your mortgage, a part proportional to the amount of your house you use exclusively for business.
So we are back to, “just buy a house if you can’t afford rent.”
What are you talking about? That doesn't make any sense whatsoever, and it certainly doesn't arise from my arguments.
Look, you're entering into this from the assumption that I'm suggesting you defraud the government. That is completely untrue. What I am saying is that "business" is a much broader category than you seem to think. A garage sale can certainly be a business activity. Re-selling merchandise online can certainly be a business activity. There is no explicitly defined line on how many business activities you need to perform, nor a explicit time period in which you need to perform them in order to consider yourself a business. As long as you approach it with the intention of (eventually) becoming profitable - even if you can't figure out how to do that right now - it is a business, and you are entitled to claim it as such.
It is the epitome of foolishness to conduct business activities without declaring them to be "business".