Your pro probably finished with a 100g maybe 120. But he didnt use an oribital. Resand the area back to barewood and besure that no water or anything touches the floor before staining. Especially sweat. If you can grab a piece of 100g sand paper and before you apply stain. Hand sand the area with that paper. Orbitals sanding and pro sanding do different things. Then i would stain just a small area and see if its close enough to a match. If not then resand and try water popping the area. That may do it. Its better to have it be a tad off then way off. You likely wont get it perfect. Age is a factor even though its only been a couple yrs. If you go to a hw distributor you might get some flack but if your pro floor guy wint sell it to you then go online. Theres no special permits or licenses you need in order to purchase or use it.

I think the misinformation was about screening and recoating a site finished and doing a board replacement. On site finished if you have a problem its much harder to do a single board replacement and have it blend. Most times you would have to resand the entrire floor to make it look good. With factory fiished a single board could be replaced without resanding adjoining areas. Either could be screened and recoated without sanding. Comments about factory finishes scratching are sometimes due to the fact that with multi coat products the almunium oxide is left off the top coat. It tends to look milky and the idea is to make the top coat easy to repair when scratches occur so its often pure urethane with the AO below the top coat.

We never would put wood directly on a concrete floor, instead we'd install sleepers, plywood and then lay the wood on that. Here in the northeast, with weather changes and humidity problems, putting wood right on concrete is not good practice. Also, wood swells and shrinks with changes in humidity and temperature. Gluing the floor down it would seem to me would cause it to possibly split or swell at glue joints, although I do realize that manufacturers of engineered flooring claim this does not happen :)

Sure you can! We patched our hardwood at a number of places including where we took out fireplaces, expanded doorways, and where we moved walls. It is easier to do if you only have to worry about lining-up one side (if the other end hits a wall for example and can be hid under baseboard). We did have places where we had to butt the new piece up to exisiting wood on both ends- it just takes a bit more precise measuring. In both cases we followed these steps: Prepare the opening: 1. Identify where the seams are or mark where to cut (if the seam is too far away). We marked our seams with masking tape- be sure to stagger the seams. 2. We used a large piece of steel as a guide and routed any new 'seams'. Be careful not to cut past the one piece of hardwood you are working on...I speak from experience. Use a corner punch and hammer to clean the edges. 3. Using the router, rip the hardwood down the center to the seam- pull out and discard. 4. After you have prepared the opening, measure and cut your replacement pieces. We had a machine to cut the tongue and grove ends but if you don't have one you could chisel off any tongues that were a problem. Slide your new piece of hardwood in and attach it. You may have to shim under pieces or edges to make them line-up correctly. For the final piece you will probably need to chisel off or cut off the tongue to get it to snap in place. We tacked the final piece with small finish nails. The process isn't hard- just time consuming and VERY detail demanding. I'll try to dig-up some pictures of the process if you are interested in seeing them. (I'm on a new computer and my stuff is still on the old one). Hope this helps!