What this buyer is actually deciding
Martingale-style systems increase exposure after losses in an attempt to recover. That can create a deceptively smooth win history until a loss sequence becomes very large. Non-martingale does not mean low risk; it only removes that recovery mechanism.
What to verify before paying
Look beyond vendor labels. Check lot-size sequences, simultaneous exposure, averaging behavior, maximum equity drawdown and whether losses are closed rather than carried forward through recovery layers.