There are the general contractors, but then you have the specialty contractors such as roofers, tub refinishers, carpet guys, railing & stairs contractors, floor refinishers, etc.
There are a lot of people who claim to be roofers, but that is partially because they are attracted to the margins. We have used one guy for years who used to work for one of the major companies in the area and is now on his own, so he has lower overhead and is a lot cheaper. But, because of their training, he is good.
If your tub has a nick or scratches you might want to contact a tub refinisher. If it is a high end house, get a new tub. If it is for a rental or a lower end house you should look at the refinish option. When they are finished it looks almost like new.
Carpet can cover a lot of sins. If there is a floor that is in too bad a shape to be refinished, or it has 2 or 3 layers of tile / linoleum on it, you can put down a thick padding and then carpet and save a lot of money compared to redoing the floor. Ask to see an example of their work so you can see if their seams are visible or not.
Railing & Stairs Contractors
If you can find a good metal fabricator they can really add value to the place you are working on. If a set of stairs need to be replaced, you can get them to put in a set of modern looking open riser stairs. This can be a real wow factor. At the same time if you are replacing railings, you can have them include baskets or scrolls or twists in the spindles which aren’t much more expensive but give a much fancier look and ads value to your rehab so you can sell it for more.
Finding a good one can be hard but worth it. Try calling or stopping in to several companies that sell flooring. They usually know floor refinishers and can recommend several to you. Don’t refinish a floor yourself. But, do refinish the floor if it needs it. It can make a dramatic difference in the appearance of the house. The problem is that the sanders are tricky to handle and can seriously gouge and damage the floor. (I would love to know how the professionals learn to do it in the first place.)