Buyers try to negotiate before giving you any commitment – A) let them start B) don't let them start C) buy time?

Let them Start, Because if customer is negotiating that means he is having some interest in product.
but this doesn't mean he will be purchasing the product/service at that time.
but later whenever there is any requirement customer will definitely think of you.
Definitely this add a prospect in your list.

Let them start because if they start that`s mean they are interested even not for now .

if is a customer is negotiating or bargaining in most case he is showing interest.

manage negotiation or bargaining well,aim at win win situation if possible, after all we need this customer for future sales,referals,leads...etc.

Let them start.

As every one said A is th right answer , products are meant to be sold, in sales most commonly we start with a contact and finish with a contract and in between is the time of process there are various stages in process time depending on industry , products and management policy , usually negociation happens after customer likes your product ,so giving him a chance to negociate will mutually help you and the customer to understand each other , once negociations are done it can move on to the next level

A

If you dont let them start then there is no chance they will negotiate and negotiation is step forward to closing a deal because if there is no interest in buying /procuring the product/service there is no chance negotiations will start . If you buy time actually you are allowing customer to think about other options which is your competition , if iron is hot just it hit it right position I guess you heard this so same way when buyer is mood for negotiation there is chance for a sale so grab the opportunity waiting game is not proactiveness

Knowing how good is your product to their need is the key factor in knowing which line you should take.