Sales Rep fills out form on behalf of lead...

We had this issue with some of our event campaigns, our reps wanted to sign up for the prospects that they spoke to in person. I'd love to hear of a good solution or workaround.

The sales rep needs to clear their cache after each form fill to remove the cookie.  in the future, if the lead converts on their own Marketo will merge their anonymous browser history with their lead record.  The key if for the sales rep to clear cache.

We don't have reps filling out the event form due to the cookie.  We actually sync the SFDC campaign to marketo and have the reps 'RSVP' the lead by changing the campaign status in SFDC.  The sync will then trigger the rsvp confirmation email from Marketo.

Suggestion that the form is specific to the Sales Reps.

You could also have a Thank You page, that when the rep clicks "enter new lead" link/button, there is a Javascript that deletes the cookie or cookie values.

Also, on the form I would disable autofill.

However, if the rep just reloads or clicks the back button you could get the cookie issue.

Therefore, on the page (Landing page or otherwise), I would create an script that on page load will delete the cookie!

Disable the munchkin tracking for the landing page containing the form and the thank you page. That way no cookies will be set.

Note: This can only be done on the landing page template, not in the landing page editor.

We have a LP Template for lead capture at events that is meant to be used over and over again. It removes autofill but I'm going to ensure that the munchkin tracking is turned off as well. Great ideas guys!

I've told reps before to use incognito windows, that will prevent cookies.

This common pattern is called "referral form" and there are many, many posts on this.

Manual interventions like clearing cookies from your browser settings and opening incognito windows are ​not​ necessary to make this work. 

And only disabling Munchkin tracking on a landing page does not mean that a cookie will not be sent with a form post from that page, because by default Munchkin sets cookies at the parent domain. Those cookies are available to all pages under that domain (including all your LPs and your corporate website) so a previously set cookie will still be sent with the form, unless you do this right way.  Disabling Munchkin tracking is only expected to do exactly what it says: it disables the tracking of Visit Web Page ​and ​Clicked Link​ events from that page, not forms.