Marcus used Sweet Pete as a spy

I seriously doubt it. I think it was exactly what we saw: the caramel sucked and Pete came in to show them how to make good caramel.

I rather thought that Marcus is someone who tries to force peoples real personality to come out. Pete was there to truly help and he did, but these girls clearly didn't wanted to take advice (from two men). That was the point of the whole thing.

Pete doesn't need help in marshmallow recipes. He has a big commercial kitchen, no drama and the money to try out 100s of recipes. He can just order a huge box from them and then try to clone everything without stepping a second into their kitchen.

Marcus said somewhere that fancy Marshmallows online could be a 2-3 million business, if done right. I wouldn't wonder if Pete comes out with his own recipes in the future, but made completely different. And has the guts to stick to the plan, instead of making everything political.