Tax claim on Gumtree purchases

I have an investment property and try and do cheap repairs as tenants will always break something anyway.

Recently I explored second hand sellers, through local paper or Gumtree. How does one satisfy the invoice requirements when buying from individuals?

I specifically asked the seller in link below whether he/she can give an invoice but that person stopped responding. I hope I didn't unnecessarily scare him!

Or is just printing the ad sufficient?
When I buy anything second hand from trading post gumtree etc. I print the ad and make up a receipt Thant basically says

Date... I, (name of owner) hereby acknowledge the sale of (item)
to (my name) on (date of sale) in the amount of (sale figure).

All payment has been received.

Signed (seller)

Just don't forget that there is no GST on second hand goods.
Most items sold on Gumtree would be from unregistered sellers.

However assuming that we are talking about residential rentals then no GST can be claimed anyway as these are input taxed acquisitions.