I followed your suggestion and asked my electrician for a spec sheet. It's a Tesla Backup Gateway 2. I contacted Tesla. They told me the Backup Gateway 2 is now included with the powerwalls. My electrician contacted his warehouse and verified it is included. He removed it from the estimate. Tesla also told me the web site is run by a computer and is not accurate. She told me when I click on place your order asks for a $100 deposit that is fully refundable. After placing the order the Tesla engineers are going to create three different estimates for me to look at.
1. I'm guessing the new Tesla estimate is going to go up.
2. I am a fan of having only one company to deal with so there isn't any finger pointing.
3. I don't know how to obtain/apply for referral/loyalty credits.
You are obviously free to do whatever you want, however if it were me, there is zero (less than zero) chance I would ever consider going with that electrician you mentioned, after they included a $4800 line item on your order, seemingly doubled down on it when you asked, then only removed it after you pointed it out again and they then "checked with his warehouse" or whatever.
That electrician / company is not versed well enough in Tesla equipment for me to consider them, even for a second, based on what you posted here. You also likely want to get apples to apples quotes, instead of a quote for solar + powerwall from Tesla and a quote for just powerwalls from some other company.
I would tell that electrician "thank you for your time, I appreciate the quote and have decided to move in a different direction", and possibly get quotes from some other company instead of that one, and for like for like (solar + batteries).
I am not against third party installers at all (far from it), and going direct with Tesla has its own challenges (see the customer service thread stickied here for some challenges people have had), but in general, Tesla tends to be the least expensive if your home is a fairly easy install.
If you are looking at third parties, you want a competent one, and Im sorry but for me, an electrician adding what amounts to a 5k line item on a quote for hardware that is included, then doubling down on telling me "its not the same thing thats included" and only pivoting when I directly pointed it out, is a complete. utter, 100% non starter to do business with.