We need a sample return mission to be sure.
AFAIK, no such mission is planned.
By the time the other side has to pay me $100 when we find life, that amount will probably not be enough to buy a cup of coffee.
I will be amazed if we do not find microbes.
Remember the Allen Hills meteorite? I met with the scientists who wrote the paper on the nano-fossils. They had pretty strong proof. We found almost identical nano-bacteria two miles deep in basalt on Earth.
Dr. Arthur C. Clarke has pointed out that we see objects in photos from Mars that look like seashells, root systems, and seeds. He says we already have proof of past life.
So, you won’t take the five year bet? 3 ounces of silver?