I bought a B&Q tiling DVD from car boot sale a few years ago it showed the basics of setting out around doors, windows etc and the use of a gauge rod.
It of course promoted the use of the nasty B&Q tubbed addy and didn't mention you can't use it on big tiles!
I'll never forget I was in the builders merchants once and a guy came in with a dot & dabbed tile that had fallen off. He came in to complain about the ready mixed adhesive he had bought.
The tile was way too big for that addy, he had PVA'd his smooth new plaster and placed 8 blobs on each tile, they nearly all came loose while grouting. The addy on the tile (2 weeks fixed) was still moist and the PVA had come off and was sticking to the flat smooth blobs of the back of the tile.
He said the adhesive was faulty and wanted a refund, the counter rats said we've never had any problems before!!
When I told the diy'er his mistakes and that the adhesive he had bought was not suitable for the size of tile and that PVA was a no no, he was gratful but had never heard of powdered adhesive.