Quite often spot that in South African racing. One day I picked out 5 horses and guessed they would be around 5 to 10/1 with one i most fancied called Tiger right being about 8/1. When it came to having a bet it was priced at 100/1. So £10 ew plus put in all multiples. It won by 4 lengths and was returned at 13/2.
The guesser compiling the odds probably saw there was £2 available to back at 100 on Betfair and decided that was the price it should be.