The absolute best and possibly the only way to avoid improperly fitted equipment is to own your own equipment. Some are on tight budgets these days - I get that. There are still several ways to get equipment affordable.
You can buy used equipment. There is always someone looking to upgrade their own equipment and is most likely willing to sell their old equipment to off set the cost of purchasing new equipment for themselves. The more you are around divers the better chance you run into someone that will be in a position to do just that.
You can start browsing for equipment on the internet. The internet is loaded with information. However, do not randomly buy used equipment via internet. You run the risk of buying bad equipment and it costs a lot to get it working. Plus if you bring it into the local dive shop, they will charge you for every little thing. For example, check the used regulator to see if it’s operating properly, add hoses or even rearrange hoses. This can cost you up to $100.00 or even more. It's the reality of purchasing the scuba equipment from an outside source or via internet. If you purchased from a local scuba store they are less likely to charge you for every little thing. Yes you pay more for the equipment but you get much more than what you purchased. You get customer service and manufacture warranties. Equipment purchased from the internet typically does not honor manufacturer’s warranty. The service from your local dive shop is worth it alone. Especially if they have a pool and you get to try your own equipment out and for any reason you are not satisfied you will get a credit towards an exchange.
Note: You can buy equipment via internet and get it new out of the box. Some of these venders are getting around a local dealer support. Sometimes it's harder to get support and maintain the warranty. Yes, it works, but it can be a hassle compared to just going to your local dealer.
Another way is to do layaway. Most people are familiar with layaway programs. Typically they are interest free and you pay what you can afford over time. If you dive locally, the best time to do this is in the winter so you can have the equipment by the time the dive "season" starts.
You could ask friend sand family to get you a gift certificate from your local scuba diving store instead of presents for your birthday, anniversary, Christmas and any other gift giving occasion. This could help a little, or a lot.
Otherwise there are programs that you can qualify for with credit. Some will do 90 days same as cash. However, you better pay the balance in 90 days or there will be hefty fees/interest (I'm not giving credit advice, just casual conversation).
Nothing will improve your diving and make you feel more comfortable than having your own equipment. Be sure you do your homework on the scuba equipment to get a good handle on what will work for you.
These are just a few ways you can help purchase your own equipment so you can get out and going scuba diving and gain more experience. I’m sure you can find other ways to find scuba gear affordable. Just keep your eyes open and your mind open to the opportunities to get scuba equipment.