All the products should probably go in one table. Unless their attributes are so different that they need their own table for their type.
In other words. If you sell cars and washer machines, I would put them in 2 tables. But if everything you sell really only has a product type, description, wholesale price, retail price, I would put them in the same table. If it's the same products with different vendors, then you may want to add a vendor table
For creating invoices, you should follow the basic Invoice relationship setup
LineItems is a join table that you will put in a portal on the Invoice layout. LineItems will look-up products to add to portal. Customers will just be a dropdown of customer names to populate the invoice.
Even if selling Cars and Washing machines, you should have a single table of at least the price and product ID as that makes things much easier to work with. If you then need to record other info that is very different for different categories of products (or services), use related detail tables linked to your single table of product ID's and prices.