Great question. I also own several ecommerce stores and had the same questions. I discussed these urgency and credibility tactics with the Rav at length just a few weeks ago. The bottom line was that if the statement is true then it is permitted but if the statement is false it is prohibited.
So for example, stating that this deal is ‘Today Only’ if you plan on having the same offer tomorrow is a false statement and therefore prohibited. Stating ‘Only 3 left’ is also false if you have more than 3 in stock and therefore prohibited.
Many commerce sites use tools like https://beeketing.com/sales-pop where website visitors see a popup that says “Joe bought a ‘product’ 20 minutes ago”. This statement is usually only half true. Joe did buy a ‘product’ but it wasn’t 20 minutes ago. It may have been several weeks or months ago. This is how these tools work. They take data from your sales and then they create popups based on that data but to increase urgency they change the times to seem like it just happened. They then make these popups display every minute or so to make it feel like everyone is buying from the site and that things will begin selling out… This causes a sense of urgency and increases a sense of credibility that pushes you to make the purchase right away.
I discussed this specific tool with the Rav and his response was “it’s stealing” because the statement isn’t 100% true.
All these tools may be used though, if you use them honestly and keep all statements 100% true and accurate. So for example, a sales popup can say “Joe bought a ‘product’ for $50” without stating when. This statement is now 100% true and accurate and therefore permitted. You may advertise “Hurry! Huge Sale Today” without saying “Today ONLY” and then the statement would be 100% truthful.
So as we said in the beginning, always make sure the statement is truthful and accurate and then its permitted.
Its also very important to remember that our income is decided by God and no one can ever take our income away from us. Our job is to do our hishtadlut (personal effort) and then leave the rest to God. We need to worry about doing our part and leave the outcome to God. Do not think for one second that you will lose out on your income for being honest. So long as you do your part and remain honest you will receive all the money that is coming to you which was decided by God on Rosh Hashanah.