You should never hire a cheap SEO agency unless you want to spend time undoing everything they did. Alternatively, you could spend more money to hire another SEO agency to undo what the first one did.
SEO isn't cheap because white hat tactics, like creating unique, interesting content, are time consuming. Many business owners understand SEO, they simply don't have time to do it themselves. Some don't have the time to learn how to do their own SEO, so they outsource the work. Unfortunately, when you outsource a job you don't understand, you won't know if they do it correctly.
Most SEO agencies are reputable; they grow their business by word-of-mouth and having a high client retention rate. A few rogue agencies get clients by offering low-cost SEO and doing very little work for the money. These agencies stay in business by getting new clients who believe cost is the primary consideration when choosing an SEO agency.
A low-cost SEO firm may use various black hat tactics to get their client a higher position in the search results. These strategies, such as buying links, work in the short-term, but Google will catch on and penalize the site. The client may have already left a good review before they realize what is going on. Other low-cost firms may not try to deceive clients; they merely outsource work, like content creation, to the cheapest provider. The client ends up with poorly written blog posts, which don't help their ranking at all.
The moral is; don't buy SEO services if you're not willing to pay the going rate. If you're like most people, your website is your business. It is how you earn money, so you don't want to cut corners on SEO. You really do get what you pay for with SEO. For more information click here https://www.reddit.com/r/SEO/comments/hswmzy/onemorereasonnottohirecheap/.