When you sell an option, the amount is credited to your account. You now have a contractual obligation and at expiration, you'll find out how much of that credit you get to keep. If it's a covered call position, the credit is all yours. At that time, it's the underlying that may or may be the problem.
Yeah, that was my solution too. I didn't want to use much extra money or margin but there is no way around that. Anyhow an example: I have AMD stocks and when price was at $11, I sold the 11 strike for 70 cents, and I would be happy to take that even if the stock goes higher. The stock actually went above 12 for a short period, and this was the point where I wanted to lock in my 70 cents premium, because I was guessing it would fall back. Sure enough, it did, and today it dipped below 11 bucks. I guess I could have sold just the stock and bought calls at the 13 strike price, to make it vertical calls as you suggested.
In some cases, if I sell the stock and convert to a bearish call spread, I'll also sell OTM puts at the short call's strike in an equal number. The put premium brought in will partially offset the loss on the call spread if the underlying continues up. If it drops, you capture the intrinsic value of the short call and possibly get the stock back with the short puts. This approach isn't that viable with low priced stocks unless the IV is decent.
"Six primary factors influence option pricing: the underlying price, strike price, time until expiration, volatility, interest rates and dividends." You can read a bit about it here: https://www.investopedia.com/university/options-pricing/option-price-influence.asp