Target users only when they've gained something
Sales should always be suggestive. Unless the user has something to gain from your business neither will he fill a genuine lead, nor will you benefit with such a lead. Visitors ought to consume some of your content first before they let you in their consideration set. Once you're in, the user is more likely to fill a lead if asked with a suitable context. Example: On a pricing page, you can ask them to drop a lead to get help with a customised price quote
You're essentially looking for potential customers and hence asking the same user twice is a loss on all fronts - UX, Lead Quality, Sales effort etc. We recommend using a right targeting mix with URL and engagement triggers to get to users at the right time when they're most engaged plus using frequency capping to avoid alienating users once they've decided not to fill a form and likewise setting forms to not show for a long time once a specific user submits his details to our business. Example: Using a 80% scroll targeting on an insurance plan page with a frequency cap of 2 and with setting not to show the same form anymore to the same user after he submits his details.