Assuming in your example we are still looking at £9 steps
C - Bids £75 max auction price will show as £9 as there are no other bids
B - Bids £100 max bid will go to 'C's £75 + £9 = £84 and is winning the item until a bid over £100 is placed
A - Bids £150 max bid will go to 'B's £100 + £9 = £109 and is now winning until a bid over £150
The increments are confusing as the auction always goes to the highest maximum then adds the increment, whatever it is for each item.
I am pretty good at maths, and must admit it confused me as to why every auction was not a perfect division of the value of the increment, until it was explained to me.
Martyn