I dont know which gambling site u r talking about. But, if it is BitcoinBetting.website, then it is definitely not a lie. It is pretty easy to calculate their house edge using the following formula...
House Edge in % = ((1 - (Bet Multiplier / No. of Options)) * 100)
Therefore, House Edge of BitcoinBetting.website = ((1 - (16 / 16)) * 100) = 0%
That math would check out if not for the "transaction fee" deduction which actually creates a small edge. If you were to deduct 0.0002 from the payout amount, then it would be far more fair.
In the FAQ, it's stated: "7. Why is 0.0002 BTC missing from the bet amount I sent?
A transaction processing fee of 0.0002 BTC is deducted from each bet."
This transaction fee should only apply to the payout amount, not the bet amount.
However, the way the website works is that the bet amount has 0.0002 deducted from it.
This means for a bet of minimum size (0.0005 BTC) the house edge is:
Win event [1/16]: return of 16 * 0.0003
Lose event: return of 0
ev: 0.0003
This means
you lose 40% per bet - a
40% house edge on the minimum amount. That's pretty far from a 0% house edge, don't you think?
Even at the maximum bet: 1 BTC, there's still a house edge.
If you win, you are returned 15.9968 BTC.
This does correspond to a 0.02% house edge, which is far from the 40% earlier, but it's still not 0%.
(Though it's fair enough - this amount
can correspond to a transaction fee, albeit it's a whopping
0.0032 BTC)
The deduction should only apply to the payout. Either do this, or stop advertising the website as as having 0% house edge.