We have an interesting situation at my golf club going on. On Thursday, we played the first of a two-day tournament. On the first day, the score for the team is the best net ball of two teammates. On the second day, the best net score for each hole from both days is taken for the team's score.
On the first day, several people noticed a team was playing alone, i.e. there was no marker playing with them to ensure their score was correct. (See Rule 6-6 a.) We've questioned the pro shop as to why they were allowed to play, without a marker, especially given the history of the particular two-some. We're awaiting the resolution.
If you should happen to play in a competition, and for some reason find that you're playing by yourself, you have to ask for a marker. If you play your best and shoot a low score, your score will look suspect because you didn't have a marker, a witness to your great playing. (See Decisions on the Rules 6-6a/1 and 6-6a/2.) If you don't have a marker, you will be disqualified and your great playing will be for naught.
By the way, the two-some shot a net 59, 14 under 73 par. It's too bad they didn't play with a marker, so there would be no doubt as to the legitimacy of their score.