I am very new to road bikes and have decided to buy one. The problem is both shops I have gone to said I should get a 54cm frame, even though I'm only 5'5. This seems to go against a lot of online information and my friends advice. What should I do?
54cm does seem large for you. I'm between 5'8" and 9" and ride a 54 or 55cm (and I have relatively long arms).
Some models are effectively larger or smaller than their seat tube measurement. Bicycle shop staff may have been taking that into account for a specific bike you were interested in.
Take a knowledgeable cycling friend with you when looking at bikes.
Look at the sizing charts that some manufacturers publish e.g., this from Trek. Print it out and take it with you when looking at bikes.
Sit on or ride a 54cm, then say 'that feels too big'.
Basically the size of the roadbike depends on the length of your legs. First you need to measure that and then you can decide which size you need. Furthermore the geometies of the frames also vary, so you can't compare a 54cm frame of company X fo 54cm of company Y. Always check the frame geometry. Usually, if you are more a racer type, you would choose a smaller frame and larger stem, due to better steering and handling properties of the bike. Have a look at Canyon size and positioning tool/calculator to find out which body measurements are important and should be consideren (torso length, shoulder width, ...)
If this is your first road bike then perhaps you should do one of two things:
buy from a store that has a good exchange policy. Many stores will let you return a bike in 30 days in exchange for another bike they have. This way, if you really feel it’s too large, you can downsize.
often it’s good to buy a used bike when you shift to a new style of biking. Road bikes feel very different from mountain bikes which feel different from recumbents. By buying used, you can sell it once you know what you like or dislike and what size or posture feels right. Features such as disc brakes might not be for everyone, etc.