That is the point. Custom bitcoin clients are NOT easy. Unless you know what you are doing you probably should NOT be making a custom bitcoin client.
There is nothing custom about doing bitcoind sendtoaddress and getting a txid back.
f) rely only on tx-id as absolute proof on if a payment has been made or not
[snip]
They should build off existing proven clients.
So, then how do I easily spot this with a reasonably recent standard client?