BasePayment.rb

class BasePayment
  def initialize card, amount
    @card = card
    @amount = amount
  end
  
  def process_payment!
    authenticate_merchant && make_payment
  end
  
  def authenticate_merchant
    raise NotImplementedError.new "authenticate_merchant"
  end
  
  def make_payment
    raise NotImplementedError.new "make_payment"
  end
end

StripePayment.rb

class StripePayment < BasePayment
  def authenticate_merchant
    begin
      return true if Stripe::Merchant.authenticate ENV['STRIPE_API_KEY']
    rescue Stripe::MerchantError => e
      Rails.logger.error "Cannot establish connection between Merchant and Provider."
      return false
    rescue Stripe::ProviderUnreachable => e
      Rails.logger.error "Provider unreachable."
      return false
    end
  end
  
  def make_payment
    begin
      return true if Stripe::Payment.process! ENV['STRIPE_API_KEY'], @card, @amount
    rescue Stripe::PaymentUnprocessable => e
      Rails.logger.error "Payment unprocessable, try again."
      return false
    end
  end
end

Hello, thx for the great article!
Just my two cents about raising exceptions. I believe that better to use this one built-in exception class:

raise NotImplementedError.new 'bla_bla_bla'

intead of:

raise "Implement 'bla_bla_bla'."

Yes! I just got the same suggestion in the comments on the blog - I updated the examples. Thanks!