How to set prices including VAT for EU/B2C buyers while excluding VAT for non-EU/B2B buyers
You can set prices including VAT for EU or B2C (business to consumer) buyers and prices excluding VAT for non-EU or B2B (business to business) buyers, without needing to create duplicate products nor maintain separate seller accounts.
Approach A
This approach would use the &amount= parameter on your button URLs to boost the price on your VAT-inclusive purchase button URLs. With this approach, your products' Price settings would be the non-VAT price, so you'd just use your regular button code for non-EU or B2B buyers. For EU or B2C buyers, you'd provide separate buttons for the exact same products, but these button codes would include an &amount= parameter to add VAT overhead to the item's base Price setting.
For Add to Cart buttons, the specified &amount= value gets added to the item's base Price; however, for Buy Now buttons, the &amount= value overrides the item's base Price setting (as long as that value exceeds the base Price) -- e.g., an Add to Cart button that adds an extra 12.34 to the base Price would look like this (where XXXXXX is your E-junkie Client ID and YYYYYY is your product's Item Number):
<a href="https://www.e-junkie.com/ecom/gb.php?c=cart&ejc=2&cl=XXXXXX&i=YYYYYY&amount=12.34" target="ej_ejc" class="ec_ejc_thkbx" onclick="return EJEJC_lc(this);"><img src="https://www.e-junkie.com/ej/ej_add_to_cart.gif" border="0" alt="Add to Cart"></a>
Approach B
This different approach would use our Variants having individual price/weight/stock/SKU feature, where you'd set up each product with Variants to determine VAT-inclusive vs. non-VAT prices. This has the advantage of allowing you to update prices in Seller Admin later without having to edit any button codes already in your page, as long as you don't change the corresponding option values for your Variants. To follow the examples I'll provide here, you'd want to familiarize yourself with our Variants configuration as described here -- e.g., a product with an VAT-inclusive price of 30.00 and non-VAT price of 25.00 could Define Variants with Option 1 Name = "Incl. VAT" and a configuration like this:
VAT,30.00,,,Y,,
NOVAT,25.00,,,N,,
A neat trick here is that you don't need to depend on buyers to select the proper product option from a dropdown menu; rather, you can provide separate Add to Cart buttons for EU/B2C and non-EU/B2B buyers that hard-code the proper option into their respective button URLs (see this tutorial for a more detailed explanation of this general technique) — e.g., following the example Variants configuration above, your Add to Cart button for EU/B2C buyers would look like this (again, where XXXXXX is your E-junkie Client ID and YYYYYY is your product's Item Number):
<a href="https://www.e-junkie.com/ecom/gb.php?c=cart&ejc=2&cl=XXXXXX&i=YYYYYY&o1=Y" target="ej_ejc" class="ec_ejc_thkbx" onclick="return EJEJC_lc(this);"><img src="https://www.e-junkie.com/ej/ej_add_to_cart.gif" border="0" alt="Add to Cart"></a>
Implementation
You could put these buttons side-by-side on your sales page and let buyers choose to click the EU/B2C or non-EU/B2B button, but that approach could be prone to buyer error or dishonesty. A better approach would have separate sales pages for VAT vs. non-VAT buyers, so when buyers arrive on your site or click your Shop/Buy/Store/etc. link, they would then click whether they're in the EU/B2C or not to be directed to the appropriate sales page.
For greater sophistication, this could even be automated with custom scripting in your site — e.g., the buyer's location choice could set a cookie in their browser that determines which sales page they see, or a single sales page could read that cookie to dynamically append the &amount=, &o1=Y or &o1=N parameter to all the Add to Cart URLs on that page, or your scripting could even use GeoIP to determine the buyer's location automatically based on the IP address of their connection. However, setting up such custom scripting is beyond the scope of support we can provide, so if you'd want help with that, we can recommend the independent developers for hire listed here.