Sometimes I am guilty of it, taking down an airsoft gun but no idea on how to put things together back again. I usually take photos and notes per step when disassembling one to ensure that I can reverse the process using my documentation, but it's still best if a video from the manufacturer on the assembly and disassembly of their product is provided.

Here is ICS with their assembly video of their ICS M1 Garand AEG. Too bad it's not the same as the real one where you can do both in seconds.