To gather information about the network without causing detection mechanisms to flag the reconnaissance activities, the penetration tester should use sniffing.
Sniffing:
Definition: Sniffing involves capturing and analyzing network traffic passing through the network. It is a passive reconnaissance technique that does not generate detectable traffic on the network.
Tools: Tools like Wireshark and tcpdump are commonly used for sniffing. They capture packets and provide insights into network communications, protocols in use, devices, and potential vulnerabilities.
Advantages:
Stealthy: Since sniffing is passive, it does not generate additional traffic that could be detected by intrusion detection systems (IDS) or other monitoring tools.
Information Gathered: Sniffing can reveal IP addresses, MAC addresses, open ports, running services, and potentially sensitive information transmitted in plaintext.
Comparison with Other Techniques:
Banner Grabbing: Active technique that sends requests to a target service to gather information from banners, which can be detected.
TCP/UDP Scanning: Active technique that sends packets to probe open ports and services, easily detected by network monitoring tools.
Ping Sweeps: Active technique that sends ICMP echo requests to determine live hosts, also detectable by network monitoring.
Pentest Reference:
Reconnaissance Phase: Using passive techniques like sniffing during the initial reconnaissance phase helps gather information without alerting the target.
Network Analysis: Understanding the network topology and identifying key assets and vulnerabilities without generating traffic that could trigger alarms.
By using sniffing, the penetration tester can gather detailed information about the network in a stealthy manner, minimizing the risk of detection.

Search engine analysis enables the tester to gather publicly available information about the target, such as office addresses, employee details, and associated locations, making it the most effective method to identify where a designated target is located.

An HTTP 403 response indicates access is forbidden, often due to server-side filtering such as user-agent restrictions or compatibility controls. Using a legacy browser can bypass such filters if the application allows access only to specific or outdated user-agent strings, enabling the tester to access the page.

Presenting the documented methodology shows exactly how each vulnerability was identified, demonstrating that industry-standard procedures and controls were followed, which helps reassure the client of the findings' validity and de-escalate their concerns.

https://www.netscout.com/what-is-ddos/slowloris-attacks
From the http-title in the output, this looks like an IoT device with RH implying Relative Humidity, that offers a web-based interface for visualizing the results.