When you are assigned a rink to play a match you will be able to detect visually whether the playing surface is smooth. What will not be obvious is whether the areas to the left and to the right are equally level. Usually they are not the same. That is why the bowling angle (the bias) may not be the same on each hand.
If practice ends are permitted there is a method to test and find which side of the rink is the closest to being level. Here is how it is done.
With your first practice bowl, with the small ring pointing to the left, deliver the bowl as close as possible down the centre line. The bowl will curve to the left and finish closer to the left boundary (#1 in the figure).
With your second bowl deliver it with the bias towards the centre line and an aim line directed precisely towards where the first bowl finished. If the green on the left side is essentially flat, this second bowl will draw back almost exactly to the centre line (#2 in the figure).
Your third and fourth bowls are played towards the right side of the rink in the corresponding way ( #3 and #4 in the figure). If the green on the left side is essentially flat, the second bowl will draw back to the centre line. If the left and right sides of the green are both essentially flat, bowls two and four will both have curved back and will have finished close to the centre line. In the figure the green on the left side must be essentially flat but on the right side it seems to indicating that it slopes down and away from the centre line.
Usually the flatter side of the rink is the most dependable hand to prefer in your play on but the other hand is by no means unplayable, it just requires more trials to discover the proper aim line.