After thoroughly investigating this whole situation from multiple viewpoints, it is clear that Saif was an intrusive and irresponsible guest. Saif's gripe with the front door lock could have been avoided if he had read the check-in details prior to arrival, which includes instructions on how to open the door. Admittedly, the door and lock are a little old, but still completely functional and none of the dozen-plus prior guests have ever had an issue. Engineer or not and age aside (both irrelevant, 3 engineers live here) it's no coincidence that Saif had problems with the door since he neglected to read the instructions.
Saif came home at 3am on the second night he stayed here. My roommate was asleep, but was awoken when his dog started to bark, sensing someone at the door. He woke up and let Saif in (who had previously broken his keys trying to use the keys in the wrong locks). It was not a big deal initially, but my roommate later noticed that Saif had sent him a very rude text message asking him to open the "f-ing" door since he had locked himself out.
The next night, Saif returned home at 5am. This time, there was no rude text message, but my roommate's dog woke up barking again. Once more, my roommate had to let Saif in, likely due to his alcohol consumption and impatience with the lock. In the morning, my roommate tried to have a chat with Saif, expecting an apology. Instead, Saif became antagonistic, accusing him of being a poor host since he was annoyed with being woken up in the middle of the night twice in a row. My roommate responded assertively and told Saif off for his actions, but Saif's story about him using profanity and threatening body language is a complete exaggeration, bordering on a lie.
Aside from all of this, MOST GLARINGLY: Saif left the front door wide open one morning, left our toaster oven on another morning, left an iron plugged for days until i returned to my room, and had another unplanned guest stay with him throughout the trip (without paying the fee). It is clear that Saif doesn't understand the culture and etiquette of being an Airbnb guest.