To answer your question bedhedred in my experience they encourage you to walk rather than have a shit punt. Most agency sites do actually say this or words to that effect.
In the scenario that you do walk they immediately upsell the other available SPs as soon as you do walk. All they care about is their commission. They don't give a flying fandango which SP they get it from.
It's not in their interests long term to have disgruntled punters. The above is the case for an experienced OP anyway.
If you complain after the deed is done there's very little chance of any recourse.
As they used to say in The News of The Screws : "I made my excuses and left" that's my motto if I'm not sure in the first 5 mins.
Think of Diva as Uber and the SPs as minicab drivers. That's how it works IMO. YMMV may vary (especially if you don't use Waze

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