Courts have modified the "certainty" rule into a more flexible one of "reasonable certainty." In such instances, recovery may often be based on opinion evidence, in the legal sense of that term, from which liberal inferences may be drawn. Generally, proof of actual or even estimated costs is all that is required with certainty. Some of the modifications which have been aimed at avoiding the harsh requirements of the "certainty" rule include: (a) if the fact of damage is proven with certainty, the extent or the amount of therefor may be left to reasonable inference; (b) where a defendant's wrong has caused the difficulty of proving damage, he cannot complain of the resulting uncertainty; (c) mere difficulty in ascertaining the amount of damage is not fatal; (d) mathematical precision in fixing the amount of damage is not required; (e) it is sufficient if the best evidence of the damage which is available is produced . . . .M & R Contractors & Builders, Inc. v. Michael, 215 Md. 340, 348-49, 138 A.2d 350 (1958) (regarding damages for lost profits in breach of contract case). See also David Sloane, Inc. v. Stanley G. House & Associates, Inc., 311 Md. 36, 40-41, 532 A.2d 694 (1987); Impala Platinum Ltd. v. Impala Sales, Inc., 283 Md. 296, 330-31, 389 A.2d 887 (1978); Stuart Kitchens, Inc. v. Stevens, 248 Md. 71, 74-75, 234 A.2d 749 (1967); Della Ratta, Inc. v. American Better Community Developers, Inc., 38 Md. App. 119, 139, 380 A.2d 627 (1977) (all reiterating same in context of lost profits from breach of contract). See generally Charles T. McCormick, Damages 26 and 27 (1935) (discussing the certainty rule as to damages and the modifications thereto); 25A C.J.S., Damages 162(2) at 80-81 (1966) ("Proof of the amount of loss with absolute or mathematical certainty is not required").