Since I've only ever trained alone I know what I can handle in terms of not being able to get the weight back up. Every once in a while I'll push to far and it requires bad form to get the bar back up on a bench press.
Never tried a 1RM, probably wouldnt do that unless I had a partner. I once had a guy spot me for decline DB Presses, dude put the DB's in my hand all awkward, gave me both DB's at the same time, are you kidding me bro, how the heck am I suppose to grab the DB when your holding both of them by the handle?!! That gave me a bad taste for using strangers to spot and help you.