Re: I'm bored, let's debunk another martingale gambling strategy! New experiment 🏇!
The problem with all betting exchanges is low liquidity. It's probably not a problem to place a $5 bet there (and only on popular markets), but larger amounts will be problematic.
Depends on what events you choose.
Major ones in football, basketball have enough liquidity for anything, even for smaller events, especially tennis.
For horse racing, especially lower-level grade 4-5 races, exchanges are a no-go; I've seen races starting with less than 100 euros matched on the board.
And anomalous if you think about the mathematical expectation 
I think the results are biased by the fact that bookies would have to get a lot of things wrong continuously. I checked back and there were 6 chains of 5 wins versus 2 of 5 losses. I'm genuinely curious how the statistics will change once the jumping season starts in two months, results there are far more unpredictable than flat racing.