Saying that it's for strictly local use so it doesn't have to be robust is, as I'm quite sure you're aware, no defence.
Not sure what you're alluding to, but what I am doing is a project where I need some very basic communication between some Pi's and my computer. This is not release code, but tooling for my own needs. For data 'robustness' I will indeed be implementing a basic checksum such as Fletcher and keeping the blocks small (256 byte or so) with a mechanism to signal bad blocks back to the sender. Not sure if I'll throw block serial numbering and recovery on top of that. The files I'll be transporting are pretty small generally.
I could do something basic where the sender sends an arbitrary number of blocks, say 10 and not send anymore until it receives a 'pass' for a block by seq number. If it receives a pass, then send a new block; if it receives a fail, then send a replacement for the block that failed. If a timeout expires, then abandon the transfer.
Or, given that the file sizes will be pretty small (several MB at most), just 1 block at a time, repeating blocks if failed and a general timeout.