Explanation
According to the Trailhead module on Get to Know the Marker Layer Builder4, creating a marker layer follows the same process as creating a Salesforce report. Therefore, to test a marker layer and ensure Salesforce Maps is displaying the correct number of results, a user can create a Salesforce Report to match the Marker Layer Builder criteria4. This way, they can compare the results from both sources and identify any discrepancies or errors.

Explanation
The implementation team is responsible for business and IT sanity testing post deployment to production.
Sanity testing is a type of software testing executed on the stable build of an application with minor code changes. It is also known as surface-level testing. A sanity test is performed to ensure the application works as expected after the bug fixes or changes in the code1. The implementation team, which consists of developers, testers, and business analysts, conducts sanity testing to verify the functionality and performance of the application after deployment2. The project manager, the Salesforce support team, and the customer are not directly involved in sanity testing post deployment.

Salesforce Maps can help marketing teams to plan and execute customer events by allowing them to plot leads and contacts on the map, select a specific location based on the most populated area, create a shape around the selected area, and use mass actions to add leads and/or contacts to an existing campaign. This way, marketing teams can target the most relevant and engaged prospects for their event, and invite them using a marketing campaign. According to the Salesforce Maps documentation1, users can create layers of leads and contacts on the map, filter them by various criteria, such as Pardot score, industry, or account type, select a point of interest as a reference location for the event, such as a hotel or a conference center, draw a shape around the point of interest to define a boundary, such as a radius or a travel time, aggregate the data of the leads and contacts within the boundary, such as the average score or the number of attendees, and use mass actions to add them to an existing campaign in Salesforce2. This process can help marketing teams to optimize their event planning and execution, and increase their attendance and conversion rates. Reference:
1: Using Salesforce Maps with Pardot for Marketing Automation2
2: Create a Journey Campaign | Salesforce Trailhead Module3

A user can plot a Live Layer in Maps for three main purposes. One is to dispatch the nearest driver to a service call, which can help optimize routing and scheduling. Another is to validate a driver's location in the event of an emergency, which can help ensure safety and security. A third is to see any occurrences of speeding events for a given Live Asset, which can help monitor performance and compliance. These purposes are explained in the Create Live Layers document.

One way to ensure that the reps are only focusing on marketing qualified leads in the field is to create a data set with filtering to include only those leads that meet the criteria for marketing qualification. A data set is a collection of records from Salesforce that can be plotted on the map and used for routing and scheduling4. To create a data set, the user can go to the Data Sets tab in Maps Advanced, click New, and select the object type, such as Lead. Then, the user can choose a report or a list view as the data source, and apply filters to narrow down the records based on various attributes, such as Pardot score, industry, or account type. The user can also select which fields to display in the data set, such as name, email, or phone number. After creating and saving the data set, the user can plot it on the map and see only the marketing qualified leads in their territory5. This way, the reps can focus their efforts on the most relevant and engaged prospects for their sales goals. Reference:
4: Create Data Sets | Salesforce Help6
5: Plot Data Sets | Salesforce Help7