I think there might be a difference when a seller is selling a "couple packs or frags" opposed to single (only 1) item(s). When I do a bunch of frags, alot of the times people PM saying they are interested, but also asking questions about the frags or wanting to know if I have this or that. Those I mark down as a maybe. If I am selling a single item (like a single colony) and I get many requests I let the first person who PMed me know that I will hold it for them for 1 hour then it would go to the next person. When more people ask about the item, I also let them know someone is interested and I am giving them an hour to ask all their questions, get photos, etc, then it goes to the next person who will then have 1 hour. I almost never use "pending" unless it is a single item in a special circumstance.
I would say at least 1 in 3 people are interested but are either trying to negotiate a lower price, wonder what else I have, or just changed their mind. It can get frustrating on a seller that is trying to please everyone and not hurt feelings, especially when the seller doesnt need the money, they are just reducing what they have.
My advice would be, if you are interested in an item, PM the seller with all your questions, concerns and comments in a single PM, let the seller know you are interested but concerned about a few things you need confirmations on. Let the seller know that once your questions are confirmed that you do have the money to purchased said item and you will buy the item within the hour. And when you do get back to them do it promptly or at least let them know if you need more time. Do these things and I think you will be alright.
Just my 2 cents
Thanks for the advice!