... are sufficiently motivated and work well and reliably due to the construction boom, or are they rather somewhat negligent or overworked because of the many (potential) customers? In other words: How do you currently assess your status and your bargaining power as a prefabricated house buyer (Region Leipzig)?

What negotiating power, that hasn't existed for at least at least 5 years.

They are often salespeople and not consultants. Negotiations are limited regardless of how you build.

I thought that because most are independent sales agents and receive commissions, they are more customer-oriented, at least if they can assume that someone really wants to buy from them.

Sales representatives yes, independent no. Many are interested in the wellbeing of the customer, some less, few not at all. All are interested in their own sales commission.

They are often salespeople and not advisors.
Negotiations are limited no matter how you structure them

A good salesperson also advises well. They help to make a decision.
A good advisor also advises well. Often, however, they do not help in the decision-making process.
There are bad ones here and there.
The art is to distinguish between good and bad.

... Are sufficiently motivated due to the construction boom and work well, reliably, or are they somewhat careless or overworked because of the many (potential) customers? Conversely: How do you currently assess your standing and your bargaining power as a prefabricated house buyer (Leipzig region)?

Are you looking for the holy grail? It doesn't exist in Germany