Most any installer or contractor is going to want to do it all themselves, 100% , and they want to select the brand of panels and inverter from my experience. They also want to sell you the inverter and panels and do the install as well in a package turn-key deal because that's where they make the most money and don't have the owner telling them what to do. They want or prefer non-educated buyers is my guess. From my perspective and option, I would say either DIY or hire someone, there doesn't seem to be an in-between from what I can tell.
I bought my inverter and panels, before I did the research and the self education of solar. After watching multiple YouTube videos with various brands of inverters reviewed, I went with a Sol-Ark for my inverter because I recognized that it would work in various configurations and figured it would probably "stick" and get it configured somehow and not get returned or worse got sold for half of what I gave for it. I didn't want to go small since I saw many videos where they were upgrading their solar system, pulling stuff off the wall and buying up, many doing an upgrade several times over the course of just a few years which I saw as time and money wasteful. So, the equipment came and I was a bit scared of it and it laid in the box for 5-6 months, not knowing how I would want to use it or whether or not I would connect it to my homes existing electrical system or just use it as an isolated system for backup if SHTF. So I thought I'll just hire someone to install the equipment I bought already have here on hand. Nobody wanted to touch the project, nor call me back once they heard I had my equipment already here. So, without anyone wanting to help (I contacted 3 different local solar companies, two were an hour drive, and one was in town) and nobody wanted to touch it. That gave me incentive to learn how to do it myself and the more I learned the more I found I enjoyed it. I took it one piece at a time, first the solar panel array, then mounted the Sol-Ark to my wall, then PV wires, I then ran Romex from the load breaker over to a temporarily installed duplex receptacle just to see a lightbulb work then removed that and looked at figuring out the critical loads panel and grounding and bonding. I just kept going and putting time in until I finally got to the end of the project. I learned a lot and enjoyed the journey from start to finish and now I'm very glad I did do it myself. The end result is I have a critical loads panel, I moved breakers to it from my main service panel, I have batteries, I'm covering most of my entire home, and I am selling back to the grid which I never imagined doing. I did pay a licensed electrician $150 to inspect before I went with final connection which was well worth it because he ran the system through every scenario him and I could think of (grid down, generator on, generator off, on battery, no battery, bypass switch thrown, etc etc). All that said, I am confident that I ended up with a better install and better equipment than I would have if I had hired someone to make the decisions and do the install for me. I've seen "professional" installs where the conduit is crooked, the solar panel array is not level, and sub-quality junk like that. I know the limitations and the configuration of every square inch of my entire system, all the settings on the inverter and what they do, where and how it was all grounded, and bonded, which breakers are on solar and which are not and its limitations. Each to his own I suppose. Go with what you're comfortable with.