My company makes purchases in Poland, (my supplier charge me with the Polish VAT), I can sell in Poland without a Polish VAT number or VAT registration. What do I have to put on the sales invoice then as VAT? And what if my client has no Polish VAT-number, does that make any difference?
The sales invoice should contain information that VAT should be paid by the customer or reverse charge on the basis of art. 194 Directive 2006/112/WE. It makes a difference when the polish client has no VAT number because the Polish reverse charge mechanism may be applied only if the buyer has a fixed establishment in Poland.
So If the sales would be made in Poland to foreign non-established company (or a company without a fixed establishment in Poland) the entity obliged to pay Polish VAT would be your company.
Moreover if your company would have to register for VAT because of Polish local sales to non-established company or because of intracommunity transaction, your company would lose the ability to use the reverse charge mechanism.