Stop the Cherry Picking
Cherry picking is one of the worst offenders a sales professional can make and admitting they are doing it to someone on the marketing team is a whole other offense of its own. Marketing knows it's not efficient or effective for sales to cherry pick. This is blatant disrespect for marketing's ability to identify qualified leads and deliver them to sales. With sales calling the shots on what they consider to be qualified - whether or not it means the same thing to marketing - data is nonexistent, teams become split and opportunities are surely missed.
How to Identify a Cherry Picker
There are a couple ways to go about this if you are just unsure if you have a cherry picking situation on your hands. First, take a look at what is happening with the leads you are delivering to sales. I like to look at the create date or MQL date and compare to the status. If you are seeing MQL dates from a week ago, a month ago, and the status is still Open...you have a cherry red flag right there.
Another way is to simply ask sales how they are managing their lead flow. (Warning: Do not mention the phrase 'cherry picking'. We want to improve, not insult) Listen as they explain how they look at leads delivered to them from marketing, who they decide to call that day, how they prioritize their outreach, etc. If they are cherry picking, they will likely give themselves away.
Remove the Ability for Them to Cherry Pick
Often systems are set up where leads are being pushed into some type of CRM where sales can see everything whether they should or not - ie. MQLs vs. not-ready. When you are giving them this much visibility they have more opportunity to cherry pick because there are more options on who they want to reach out to. Oh, and your lead scoring model you worked so hard to build - that's completely meaningless. Setup a system where they can only see qualified leads delivered from marketing.
Putting an SLA in place is helpful as well. This considers why they are cherry picking to begin with. Does sales and marketing agree on what is truly an MQL? Does sales and marketing agree on the cadence that occurs once an MQL is delivered to sales? What is marketing's commitment to supporting sales with MQLs that are most likely to convert? What is sales's commitment to taking action on these MQLs?
Enforce the Process and Revisit
Once you have fixed your lead flow mechanism so you are limiting what sales can see, get on the same page with the team with an SLA or something else, you need to enforce the process and revisit it continuously.
I suggest a weekly sales & marketing meeting. Marketing has the chance to share how many MQLs were delivered, what programs are running and look at the status of everything. Both teams are held accountable in a public forum for what they have committed to do in relation to generating leads that convert and taking appropriate action to convert them.
TIP: Cherry picking is not an easy behavior to change and you may not be able to change it. You may need to make a personal decision in the end.