Are you intentionally using all three just to pick up some of the services they each uniquely offer that don't overlap, and to be able to choose which ones are strong in a particular area?  

Additionally, I'm interested in understanding typical STR fees to help estimate cash flow.If anyone is willing to share their experiences or offer advice, I would greatly appreciate it.

As the market changes, I'll have to adjust my offer accordingly.

Offered $20k over asking within a week of it coming online.

Both things are happening.Buyer agent commission is still negotiated up front with sellers although there is the option not to compensate a buyer's agent - aka have the buyer pay their agent.We also tell buyer's agents to include their commission in the offer.

These areas offer a mix of renovated bungalows, new construction, and industrial conversions, with increased demand from young professionals.

Some HIs will walk the property with you for a steep discount and tell you what they see to inform your offer.

I made an offer on a double, it turns out that it's on two parcels with two separate tax cards but deeded together. 

We are negotiating for a mobile home, he listed it at 40k, but when we offered that, he then negotiates for 42k.

It offers a learning curve that prepares you for your own property investments and builds a brand that people trust.