Buying Used and Tax Write-offs

I’m renting out my house’s additional unit and I know from my family members that I can use purchases that are going to be used for the tenant as a tax write-off. I’m a big believer in buying used, but that causes some hitches when trying to write off these purchases as most people would find it weird if you have them sign a bill of sale for purchases off FB Marketplace and Offerup.
I have two ideas for solutions but I wanted to see how ethical and/or likely they are to get me in trouble on an audit.

First (this seems a bit more far-fetched) just buy the same item new, then immediately return it and use the receipt for the item I bought used, and kept.

Second, sell the items to a friend, then immediately have them sell them back at the original purchase price, but with a bill of sale for tax documentation.
Would either of these work or do I just need to suck it up and be the weird guy showing up with a bill of sale for small items?