Buying six or more properties and dealing with tenants and contractors and lenders and town officials, you will be negotiating on a regular basis. Be prepared. Know property values and rents and municipal codes and remodeling costs before you meet.
Speak with quiet authority. Know what you want and will accept before you begin. Start the negotiation process with a lower than expected offer. Be reasonable. Don't argue or threaten. Try different angles of attack. Ask the other party to suggest a resolution. Suggest a compromise.
If appropriate, present the repercussions to both parties if any agreement is not reached. When you finalize the sale or negotiate the deal stop talking, shake hands and move on to a neutral topic.
In real estate, offers cost nothing so you can make lots of offers and do a lot of negotiating. However, don't be rushed into making an investment decision. Work at your own pace and on your own schedule. And, remember, some will, some won't, so what, next. There will always be another deal for a knowledgeable investor willing to put in the study time to find it.
If you are determined to buy your six solid income-producing properties, you will do it.