What should a marker check before a singles game starts?

If there is no umpire, you must make sure before the game starts that (law 42.1):

• all bowls have a clearly visible, valid World Bowls Stamp imprinted on them;
• the rink is the correct width, by measuring it (between 4.3 and 5.8 metres for outdoor play, and between 4.6 and 5.8 metres for indoor play, law 49.1); and
• the pegs, discs or other markers on the side banks are at the correct distances (2 metres and 25 metres from the end ditches, law 49.12), by measuring them.

Trial ends. Before the start of play one trial end must be played in each direction, on the rink the game will be played on, although for domestic play the Controlling Body can limit this to none or one trial end in one direction. As each bowl comes to rest in a trial end, a player or the marker can remove it and place it towards the front ditch (law 5.1.8).

Bowls Australia's marker pre-game role is to prepare for the game and gather the required equipment.

Source: https://bowls.com.au/get-involved/officiating-laws/marker/