Sales tax - i.e. VAT doesn't just disappear.
If a dealer has claimed VAT on the purchase of a bike from the manufacturer or importer he has to declare VAT on the full selling price.
So the new bike selling at 10,300 includes VAT of 1,766.67. The dealer may have bought the bike for 8,300 including VAT of 1,383.33. His profit is 1,616.67
If he pre-registers that bike it isn't automatically 'second hand' for VAT purposes. VAT must still be declared on the full selling price (because the dealer has claimed back the VAT he paid to the manufacturer or importer). If the bike is sold for 9,000 the VAT will be 1,500. The profit made by the dealer will be 583.33.
On second hand bikes bought as trade-ins there is (generally) no VAT charged by the seller. The dealer declares VAT on the profit margin he has made on the sale. So if you traded your bike in and got 4,000 the dealer sells it under the 'second hand margin scheme' for 5,000. His profit is 1,000 on which he must pay VAT of 166.67.