 <p>It's typically not a problem unless a) you have a lot of customers frequently making purchases (good for you! :)), and b) you change your prices very frequently</p> <p>The solution is:</p> <p>a) change prices (or, more generally, change ANYTHING) off-hours, when customers aren't likely to be using the system</p> <p>... and/or ...</p> <p>b) schedule a "maintenance window", during which you lock out user sessions in order to change prices, items and/or schema (the customary approach).</p>