title: Stripe - check if a customer exists
body: <p>In the stripe documentation they have this:</p>
  
  <pre><code>customer = Stripe::Customer.create(email: params[:stripeEmail], card: params[:stripeToken])
  charge = Stripe::Charge.create(customer: customer.id, amount: price, description: '123', currency: 'usd')
  </code></pre>
  
  <p>But I think it's wrong as for each payment we have to check if a customer exists first, I just tried it with a test account and it turned out there were created a number of different customers with the same email but different ids. </p>
  
  <p>How do I check if a customer already exists?</p>