Golf cart seat
 

I am trying to find out who will install a back seat on my golf cart
Has anyone had it done? Can you tell me who does this work, how much it costs?

I assume the cart would need better springs installed to support people riding in back.

We had ours installed by Village Discount golf carts when we bought the cart. You did not mention the make of the cart or the year, but in many cases kits are available online, HOWEVER, you are correct, that a suspension upgrade is necessary. I would guess you are looking at around $1000 for a dealer installation. Some of the mobile golf cart services may also be able to do this.