My team and i consistently make 5% to 10% every week. Its definitely possible.
Market conditions change, countries go to war, currency values can drop to 0.00, many, many, many, MANY things could happen.
It isn't possible to guarantee 5% to 10% every week in perpetuity.
Eventually the statistical probability of loss is going to occur. It might not be often, but it's a realistic possibility.
It's like a coin flip. Most people think the only viable choices are 'Heads' or 'Tails', but there are additional choices as well.
Even if you have one of those coins that has Heads printed on both sides (magicians trick coin), eventually it's going to land on it's edge.
It's most certainly a rarity that it would happen, but it does happen.
If it looks too good to be true, it's probably a scam! Let the buyer beware.