A rough idea that actually proved to be pretty accurate for me is to not mortgage more than double your annual income. I.E. if you make 50k per year don’t buy a house for more than 100k.
Yeah, my agent was a REAL piece of work, so I guess my attitude towards them is biased. A good one could be pretty helpful, but they still make more money if the house sells for more. But like you indicated, how much a couple hundred bucks would sway the average agent probably depends on the individual.