First and foremost book the income. The IRS computer audits ALL 1040s. If they show a 1099 and you don’t the examination escalated!
You do not need to provide reciepts unless you are audited. At that point, abscent proof of payment (your basis) you may be required to demonstrate with “reasonable satisfaction” the MSRP prices on your gear in the year offered for sale. The IRS will then “impute basis” and do the profit/loss calculation from there.
It is my strong conviction that you should have a CPA prepared and CPA signed return. This greatly reduces your risks. Remember these are goverment employees- they take the path of least resistance and a CPA in this case IS resistance.