I'm working as a project manager on a site with an Etsy-like shopping cart setup (allowing users to sell their products and taking a small percentage of the sale). While I expect my developer to answer this question, I figure it can't hurt to ask if anyone recommends specific gems for such a shopping set-up in RoR or financial reporting.
As far as ecommerce software for Rails goes, Spree is the de-facto standard in the Rails community.
Spree: http://spreecommerce.com, or you could use Shopify, http://shopify.com. You can build your own Shopping Cart application from scratch there, through a targeted interface.
I've tried Spree and Substruct and have upgraded the latter for Rails 2.x.
But most of us really just use: ActiveMerchant gem if there's already an existing Rails application and we just need to create a way for the client to sell the product for instance.
If you need your developer to create financial reports, there are several gems like:
fastercsv and ruby spreadsheet gem to export data into excel/csv format basic reporting of sales, orders, etc. are simple in Rails.