Hi Deb
Fronius Symo is a great inverter, and Trina make very respectable panels, as you probably know if that’s what you’ve asked for quotes on.
I know solar can be confusing, but if you are getting quotes for the same products, the choice becomes easier. You just need to do your research on the solar companies you are getting quotes from.
It’s not unreasonable to charge more for a 3 phase inverter or a difficult installation. In fact the other companies might have done so without explicitly saying it.
Read this topic for info on how to choose the right installer:
https://forum.cleanenergyreviews.info/t/ch-2-who-should-i-buy-solar-from/155/1
Hope that helps.
Marty