Private party transactions are usually the best way to get the cheapest deal. Craigslist, mtbr or ebay are common places to complete these transactions. The tradeoff for the lower price is a brick and mortar, or even online, store standing behind their product.
Over the past few years I have had my share of bad transactions. Usually it is not the fault of the seller but the product might have some small issue with it. Without a store to return the product to sometimes you can feel stuck with something that isn’t working quite right. When this happens it is always best to contact the manufacturer.
Manufacturers have a reputation to maintain. They want the riders on their products to be happy with what they bought and to use their product as it was designed. The manufacturers definitely don’t want the rider to get on mtbr or another board and rail about how their product sucks. A couple of people like that and product sales will drop.
An example of this is when I bought a pair of running shoes from a nearby Sports Chalet. I needed a new pair of shoes for an upcoming trip I was going on. I wore the shoes briefly once before the the vacation so when I was on vacation I made an interesting discovery. The black shoe had a black tongue that would slide around even when I tied the shoes on tight. After a few minutes with them on, my white socks would start peaking out and look quite silly.
Since I had gone on vacation with it, Sports Chalet wouldn’t accept it back because it was not in “like new” condition. Understandable. One quick email to the manufacturer explaining my issue and the manufacturer OK’d me to return the shoe to them and they sent me a new one, of my choice, within two weeks.
Another time, I purchased a seatpost from a seller on a local forum. The seatpost seemed to have been crushed a little as I could not get it to stay tight on my frame. This was the correct sized seatpost because I compared it to the seatpost I replaced it with. An email to the manufacturer with an explanation led to a few follow up emails before the manufacturer asked for the seatpost back and a new seatpost was sent to me.
In my limited experience, it is best to be clear, concise and level headed. SHOUTING or cursing doesn’t get very far. You can offer a solution or, what seems to work even better, ask politely: What can be done to fix this issue? By the way, I don’t know I have also found that honesty is the best policy. If the manufacturer asks if it was purchased second hand my honest answer has not deterred the manufacturer from standing behind their product.