Lots of old wives tales out there...…..a serious taxpayer would use common sense.

If there is no outside verification---------good luck with the deduction upon audit.

Outside verification---------

something such as tile map that is attested to by some one in the area who would logically know about installed tile.

Invoices or attestation from someone who installed the tile.

Pictures of the EFFECTS of a tile line---------say maybe extra-green areas------- so the hand-drawn tile map by the purchaser has some kind of verifiable support.

Anyone who thinks a "percentage of the purchase price" would stand up in a rigorous audit would also believe in unicorns...…...assuming of course that the amount in question is significant.

One can USE a percentage, but that "percentage" better be supported by something that can be verified.

A hand-drawn map of "logical" locations, supported by pictures of visible outlets, and "confirmed in writing" by an old-timer in the area (obviously a third-party), indicating that Charlie Brown "was a big believer in tiling and tiled everything in sight", is the most common way of support----------and has never failed in audits handled by us.